Seadeeps is designed for four 14th-level characters, and adventurers who defeat the monsters on this level should gain enough XP to advance to 15th level. Before running this level, consider reviewing the “Gith” and “Mind Flayer” entries in the Monster Manual, as well as the “area Ulitharid” entry in appendix A. They will help you roleplay the monsters on this level and bring their conflict in Seadeeps to life.
What Dwells Here?
Mind flayers from the Underdark have formed a new colony on this level of Undermountain, though githyanki from level 16 are determined to wipe it out.
Mind Flayers
Deep in the Underdark, a githyanki vanguard force attacked a large colony of mind flayers controlled by an elder brain. Fearing the colony’s destruction, the elder brain instructed its most loyal vassal, an ulitharid called Extremiton, to establish a splinter colony somewhere safe from githyanki incursions. Extremiton made its way to Undermountain with a group of mind flayers, laid claim to level 17 of the dungeon, and began fortifying it against attacks from the githyanki and others. The dungeon’s proximity to Waterdeep guaranteed the mind flayers a limitless supply of brains to feed on, while Undermountain’s existing defenses offered an unprecedented level of security.
Enemies at the Gates
Through methods unknown to the illithids, the githyanki vanguard force tracked the survivors of their attack on the colony to Undermountain. Having recently secured the nearby Crystal Labyrinth (level 16), the githyanki now wage war against the mind flayers in Seadeeps. Uncertainty about its own future has forced Extremiton to hold off on transforming into an elder brain. Instead, it is focused on defending the colony and destroying its githyanki neighbors. With only a dozen mind flayers remaining under its rule, Extremiton has resorted to breeding a neothelid (see appendix A) and plans to set it loose in the Crystal Labyrinth to finally wipe out the githyanki force. Extremiton is also gathering thralls of every race to help defend the colony if the neothelid is destroyed or fails in its task.
City of the Mind
Extremiton can sense intelligent creatures within 2 miles of it and is able to communicate with them telepathically. Using this ability judiciously, the ulitharid has learned a great deal about the city above and its inhabitants. Waterdeep has, in a way, captured the ulitharid’s imagination.
Extremiton intends to enslave the population of Waterdeep, but not before it fully understands this strange city and its people. The telepathic communications the ulitharid has initiated with random Waterdavians has provided it with plenty of information, but no firsthand knowledge of how city dwellers behave and react on a daily basis.
In the heart of Seadeeps, the ulitharid has built an enormous dynamo that channels the energy of an underground river to power a series of interconnected metal capsules called psipods. The illithids under Extremiton’s command have kidnapped humanoids from Waterdeep and Undermountain and put them to sleep in these capsules, which link their dreaming minds to the ulitharid’s dizzying intellect. These captives believe they’re in Waterdeep, but the city they see and experience around them is a fabrication created wholly by the ulitharid. Within this alternate reality Waterdeep, or “Alterdeep,” Extremiton appears as any character it wants. Its favorite role to play is that of Durnan, the gruff, tight-lipped proprietor of the Yawning Portal.
Extremiton can make any environmental changes to Alterdeep and observe how its captive audience reacts. Meanwhile, it continues to use its telepathy to reach out to the Waterdavians in the city above, gathering more information to better realize its version of the city.
Githyanki
After tracking the splinter colony of mind flayers to Undermountain, githyanki forces from level 16 have begun their systematic eradication of the illithid presence.
The githyanki forces on this level await reinforcements from level 16. Yaveklar, the knight in command, intends to personally cut off the ulitharid’s head and present it to her superiors. Her second in command, Lashiir, wants to see Yaveklar stripped of her command for incompetence.
Qualith Door Locks
Mounted on both sides of every door in the mind flayer colony (area areas 9 through area 20) is a burnished plate of dark, alien metal embossed with a braille-like form of tactile writing known as Qualith. Mind flayers use their tentacles to read Qualith, which is composed in four-line stanzas indecipherable to other creatures. A creature that touches a Qualith inscription, however, can receive fragmentary insight into the multilayered thoughts contained in it. A non-illithid that wants to understand a Qualith inscription in Seadeeps can make a DC 18 Intelligence check to interpret the inscription. A failed attempt results in a crushing headache and requires the creature to succeed on a DC 11 Wisdom saving throw or develop a random form of short-term madness (see “Madness” in chapter 8 of the Dungeon Master’s Guide). A comprehend languages spell provides understanding of the inscription roughly equivalent to what a mind flayer would get from it.
Each door plate is imbued with psionic energy that functions like an arcane lock spell. The Qualith inscription on the plate describes the genuflections a mind flayer must make with its tentacles to open the door. Other creatures with at least four tentacles (such as flumphs) can imitate these motions to bypass the lock, provided they can interpret the inscription. A creature must be within 5 feet of the door to open it in this way. Creatures without the requisite tentacles and knowledge must deal with the lock by more conventional means, such as a knock spell. If magic is unavailable, a locked door can be forced open with a successful DC 30 Strength (
Athletics ) check.Clever adventurers might discover that a decapitated mind flayer head, animated through an animate dead spell, can be used to access the locks.
Exploring This Level
All location descriptions for this level are keyed to map 17.
The caverns surrounding the mind flayer colony are dark and damp. The space occupied by the colony is smoothly carved from solid stone. Throughout this level, adventurers hear the constant thunder of the underground river, which is especially loud in area area 12 and slightly less so in area areas 16 through area 20.
1. Tunnel Plexus
The natural tunnel that descends from level 16 levels out before splitting into several passages that connect to area areas 2, area 5, and area 6. These passageways have uneven floors and ceilings, the distance between which varies from 10 to 15 feet. Characters who navigate these tunnels occasionally come across the bodies of flumphs slain by the githyanki.
2. Dripping Cave
Water drips from stalactites that cling to the roof of this damp, 30-foot-high cave.
3. Halaster’s Maw
Most of this 30-foot-high cavern is taken up by a gaping pit roughly 50 feet long, 30 feet wide, and 30 feet deep. Its sides slope inward so that the floor of the pit is 30 feet long by 10 feet wide. A statue of a humanoid figure lies shattered at the bottom of the pit.
The broken statue is all that remains of Aasathra Raghthroknaar, a female dragonborn adventurer who was turned to stone and placed here by Halaster to lure other adventurers to their doom (see “Pit Trap” below).
Pit Trap
A
4. Flumph Cloister
Flumphs. Stalactites cling to the roof of this 20-foot-high cavern. Lurking among them are nine Flumph. The flumphs are passive creatures that fight only in self-defense.
Secret Door. A secret door in the south wall is carved to resemble natural stone.
The flumphs telepathically share the following information with friendly visitors:
- Mind flayers have established a splinter colony on this level (area areas 9 through area 20). An ulitharid called Extremiton leads the colony. Once the colony is secure and its enemies are eradicated, Extremiton will undergo a transformation ritual to become an elder brain.
- Githyanki want to destroy the illithid colony and any flumphs they encounter. The mind flayers have spawned a neothelid—a worm-like behemoth—to defend their colony and destroy their githyanki enemies. Right now, the neothelid is trapped behind several
wall of force spells (in area area 8). - The mind flayers have captured many humanoids from Waterdeep and Undermountain, most of whom are kept as “cattle.” The rest are turned into mindless thralls in service to Extremiton.
The flumphs don’t need to enter the mind flayer colony to feed on the illithids' immense psionic energy. This cave is close enough to the colony that the flumphs can nourish themselves from a safe distance.
The flumphs are aware of the secret door but reluctant to speak of it, since they have come to rely on the illithid colony for sustenance. The flumphs would rather feed on the psionic energy of the mind flayers, who couldn’t care less, than the energy of the githyanki, who abhor the flumphs and attack them on sight.
5. Githyanki Grave
Seepage. Water seeps into this 30-foot-high cave through minuscule cracks in the ceiling, flowing in rivulets down the walls and disappearing through natural drains in the floor.
Corpses. Lying in alcoves to the east are the corpses of ten githyanki who perished fighting the mind flayers and their thralls.
6. Battleground
This area has become the main battleground in the conflict between the githyanki and the mind flayers. The ceilings throughout are 20 feet high.
6a. Cave of Carnage
Corpses. The uneven floor is strewn with the corpses of githyanki, troglodytes, duergar, ogres, and orogs, as well as eight decapitated mind flayers and two flumphs.
Githyanki. Four Githyanki Warrior with
nondetection spells cast on them lurk behind rock formations in the middle of the cavern.
The githyanki report to the knights in area area 7c. Three fight to the death to defend the cavern, while the fourth retreats to area area 7a to alert their allies.
6b. Severed Heads
Double Door. Embedded in the east wall is a stone double door sealed with Qualith door locks (see “area Qualith Door Locks"). Unless it is held open, the door automatically closes and locks.
Heads on Pikes. Seven decapitated mind flayer heads with limp tentacles are mounted on pikes in the middle of the cavern, facing the double door. (They were left here by the githyanki.)
6c. One Brave Flumph
A flumph lurks in the shadows of this alcove, surreptitiously feeding on the psionic energy of the githyanki warriors in area 6a. A successful DC 12 Wisdom (
7. Githyanki Stronghold
Two githyanki knights and eight githyanki warriors are stationed here. These githyanki are alert and won’t give up their stronghold without a fight. Yaveklar, the knight in command, carries a
7a. Arch Gate to Level 15
Light. Torches burn in iron brackets mounted to four pillars that support the 20-foot-high ceiling.
Githyanki. Four Githyanki Warrior stand guard next to the pillars.
Arch. Embedded in the east wall is a stone arch, its keystone carved with an image of a six-fingered gauntlet.
The githyanki warriors follow orders without question and have no authority to negotiate; that task falls to the knights in area 7c. A fight here brings reinforcements from areas 7b and 7c.
Arch Gate
The arch is one of Halaster’s magic gates (see “area Gates"). Its rules are as follows:
- The gate opens for 1 minute if a creature touches the arch with a six-fingered gauntlet. (Such an item can be found on level 15.)
- Characters must be 13th level or higher to pass through this gate (see “area Jhesiyra Kestellharp"). The first creature to pass through the gate triggers an elder rune (see “area Elder Runes").
- A creature that passes through the gate appears in area area 24c on level 15, in the closest unoccupied space next to the identical gate located there.
7b. Barracks
Light. Resting on the floor are two glass lanterns with
continual flame spells cast on them.Wounded Githyanki. Four Githyanki Warrior are recovering from wounds inflicted on them by the mind flayers' thralls. Each has 30 hit points remaining.
Fountain. Embedded in the north wall is a stone fountain with a semicircular basin. The fountain is carved in the likeness of a winged fish with water spouting from its mouth.
The githyanki obey the knights in area 7c and won’t accept healing from strangers without their superiors' consent.
The water spouting from the stone fish falls into the semicircular basin beneath it and drains out through small holes inside. The water is cool and clean, and serves the githyanki as a source of fresh water.
7c. Knights' Quarters
Light. Resting on the floor is a glass lantern with a
continual flame spell cast on it.Knightly Argument. Left undisturbed, two female Githyanki Knight argue quietly with one another in the middle of the room. One of the knights has a decapitated mind flayer head hanging from her belt.
The older githyanki knight, Yaveklar, commands the githyanki forces on this level. Though she is eager to slay the ulitharid and wipe out the mind flayer colony, Yaveklar is cautious and patient. She has suffered more losses than her superiors would consider acceptable, so she’s waiting for reinforcements before launching any further assaults.
The younger knight, Lashiir, stands ready to take over in the event that Yaveklar is removed from command. Lashiir is proposing to attack the neothelid in area 8, using
If the characters can communicate with the knights, they can attempt to forge a truce with the githyanki. Yaveklar orders them to slay the neothelid as proof of their worth. If the characters kill the neothelid but return to Yaveklar in a very weakened state, she takes advantage of their situation and tries to finish them off. If they kill the creature and return with strength to spare, Yaveklar agrees to let them travel through Seadeeps unmolested and will even commit forces to a joint operation to conquer the mind flayer colony. If Yaveklar is neutralized, Lashiir readily fills the power vacuum and behaves much like her predecessor.
The illithid head dangling from Yaveklar’s belt is a trophy from a recent skirmish. Resourceful characters can animate the head and use its writhing tentacles to unlock doors equipped with Qualith locks (see “area Qualith Door Locks").
Treasure
Each githyanki knight wears a suit of baroque half plate armor set with three alexandrites (500 gp each) and ten citrines (50 gp each). In addition, Yaveklar carries a
8. Operation: Eat Them All
The mind flayers have spawned a neothelid and trapped it behind magic walls of force controlled from area 16c. The illithids are waiting for Extremiton to give the order to unleash the savage creature on their githyanki enemies in Seadeeps and the Crystal Labyrinth.
8a. Neothelid’s Cave
Magic walls of force seal off all tunnels leading to this enormous cavern (see “Walls of Force” below). The floor, while uneven throughout, has been worn smooth by the creature trapped here. The cavern has the following features:
Neothelid. A 210-foot-long neothelid (see appendix A) is curled up in the middle of the cavern, waiting to be fed.
Ceiling. The ceiling is uneven—ranging in height from 60 to 90 feet—and festooned with stalactites.
Ledge. A ledge climbs the western wall to a maximum height of 20 feet. At the back of this ledge are two tunnels leading to area area 8b.
Food in the form of humanoids is delivered to the neothelid through a stone door set into the east wall, beyond which is a smoothly carved tunnel leading to area area 16a. The door is sealed with a Qualith lock (see “area Qualith Door Locks").
The neothelid is always hungry and tries to devour any creature that enters its cave. It lacks the intelligence to distinguish one kind of prey from another and feeds indiscriminately.
Tunnel to Expanded Dungeon
If you decide to expand the dungeon southward, the passage in the south wall exists but is sealed off with a wall of force.
Walls of Force
The illithids have a psionic device in area area 16c that generates the magic walls of force sealing off the neothelid’s cavern. Each wall is identical to that created by a
- The walls last until the psionic force generator in area area 16c is deactivated.
- A
disintegrate spell cast on a wall destroys it for 1 minute, after which the psionic force generator in area 16c resummons the wall.
8b. Standing Gate to Level 19
In the middle of this otherwise empty cave is a pair of standing stones topped with a lintel, carved into which is a symbol of an arrow. The standing stones form a magic gate (see “area Gates"). Its rules are as follows:
- If an arrow or a crossbow bolt is shot between the standing stones, the gate opens for 1 minute.
- Characters must be 15th level or higher to pass through this gate (see “area Jhesiyra Kestellharp"). The first creature to pass through the gate triggers an elder rune (see “area Elder Runes").
- A creature that passes through the gate appears in area area 15 on level 19, in the closest unoccupied space next to the identical gate located there.
8c. Dead-End Cave
The tunnel leading to this cave narrows dramatically, but not enough to keep the neothelid from reaching prey that flees here. The cave is empty.
9. Guard Post
The doors to this area are made of stone and sealed with Qualith door locks (see “area Qualith Door Locks"). Unless they are held open, the doors automatically close and lock. This area has the following features:
Sentries. Two Mind Flayer stand behind eight Orog (lined up in two rows of four) facing the double door to the west.
Pillars. Two stone pillars with glowing veins of crystal stand to either side of the western hallway.
The mind flayers have orders to thwart any frontal assault on the colony. The orogs are thralls under the illithids' command and defend their alien masters to the death.
10. Detention Facility
The mind flayers use this detention facility to hold “cattle”—the term they use to describe humanoids they consider a food source.
The door to the cell block is made of stone and sealed with a Qualith door lock (see “area Qualith Door Locks"). Unless it is held open, the door automatically closes and locks.
The cell block is 10 feet high throughout and contains the following:
Cells. Spaced along the corridor are ten cells with doors made of sturdy iron bars through which a Tiny creature could squeeze. Each cell door is fitted with a Qualith door lock (see “area Qualith Door Locks").
Prisoners. Three prisoners are locked in separate cells when the characters arrive: a foul-smelling troglodyte, a young male human veteran wearing the uniform of a City Watch constable of Waterdeep, and an elderly female grimlock in a soiled gray robe.
The three prisoners subsist on a slimy but nutritious gray mold delivered to them in bowls once a day by illithid thralls.
The troglodyte, Glorz, has a dinner date with the neothelid in area area 8 and, given its chaotic evil alignment, can’t be trusted to behave itself if set loose.
The City Watch constable, Ishan Toru (LG male Kozakuran human), waits to have his brain devoured by the illithids. Toru’s weapons were taken from him and discarded, and he plans to meet his death with whatever courage he can muster. He remembers being lured into an alley by a young girl who claimed her father was being accosted by ruffians. Toru was knocked
If his death seems likely, Toru asks one of the characters to take his City Watch badge and return it to his father in Waterdeep. If this is done, Toru’s mother—a renowned jewelry artist—gives that character a sapphire bracelet or pendant worth 2,500 gp as a show of her gratitude.
Ahpok, the old grimlock, has an intellect devourer in her skull. She is used by the mind flayers to lure other grimlocks to the colony to have their brains devoured. Ahpok has been unable to leave the colony in recent weeks because of the githyanki, so the illithids have stationed her here with orders to keep an eye on the other prisoners. The grimlock speaks Undercommon. Ahpok claims to know this level of Undermountain by sound, smell, and touch, and offers her services as a guide if the characters agree to set her free. If the characters follow her, Ahpok leads them to the neothelid to be killed and consumed. If the intellect devourer is deprived of its host, it teleports away to seek a new one.
11. Halaster Is Glowing
The stone doors to this chamber are sealed with Qualith door locks (see “area Qualith Door Locks"). Unless they are held open, the doors automatically close and lock. The ceiling here is 10 feet high. The room has the following features:
Arch. Embedded in the middle of the east wall is a stone arch. Carved into its keystone are three human-like stick figures holding hands.
Statue. In the middle of the room, a statue of a thin, bearded, wild-haired man wearing a robe covered with eyes stands atop a 3-foot-high block of stone. The statue is surrounded by a faint nimbus of multicolored light and points a stony finger at the eastern arch.
The glowing statue depicts Halaster Blackcloak. It is a magic trap that casts a
A
Close examination of the statue reveals that the eyes carved into its robe, twenty in all, have lids that are locked open. Casting an
Arch Gate to Level 14
The arch is one of Halaster’s magic gates (see “area Gates"). Its rules are as follows:
- If three humanoids hold hands while standing within 5 feet of the gate, it opens for 1 minute.
- Characters must be 13th level or higher to pass through this gate (see “area Jhesiyra Kestellharp"). The first creature to pass through the gate triggers an elder rune (see “area Elder Runes").
- A creature that passes through the gate appears in area area 39b on level 14, in the closest unoccupied space next to the identical gate located there.
12. Dynamo
The central feature of the mind flayer colony is a psionic, quasi-magical turbine powered by a thunderous underground river that flows through it.
River water entering the dynamo is channeled along 10-foot-deep troughs. As the water courses through each trough, it passes U-shaped, gold-plated metal conductors bolted to the sides and bottom of the trough at 10-foot intervals. The energy from the water is transferred to the conductors and used to power the apparatus in area 12g and the psipods in area areas 14 and area 15. After flowing through the dynamo, the water exits through submerged, rough-hewn tunnels carved into the sides of cisterns. The underground river then resumes its natural course, eventually emptying into the Underdark.
Creatures can walk along a stone ledge that hugs the perimeter of the dynamo. The ledge is 1 foot above water level, and four arching wooden bridges span the troughs near the central hub (area 12c). These bridges are securely bolted to the floor. The ceilings above the water collectors are domed and vary in height. The connecting tunnels between the collectors and the bridges have flat, 15-foot-high ceilings.
All doors leading to this area are made of stone and sealed with Qualith door locks (see “area Qualith Door Locks"). Unless they are held open, the doors automatically close and lock.
Underground River
The underground river on this level is swift and loud. Creatures within 20 feet of it are
deafened by the roar unless a soundproof barrier or a silence spell blocks the noise. Any creature that starts its turn in the river and isn’t anchored must make a DC 15 Strength saving throw. On a failed save, the creature is swept 60 feet downriver; on a successful save, the distance is halved to 30 feet. The river flows just as strongly through area 12 as it does elsewhere.
12a. South Water Collector
The ceiling in this chamber forms a dome 20 feet higher than the floor around the cistern, which is 10 feet deep. Water pouring in from the east travels north along a trough that leads toward area area 12c.
12b. East Water Collector
This area is watched by the ettins that lurk in area area 12h.
The ceiling in this chamber forms a dome 20 feet higher than the floor around the cistern, which is 15 feet deep. Water pouring in from the south travels west along a trough that leads toward area 12c. Excess water flows north through a submerged tunnel blocked by a 10-foot-diameter, circular iron grate that Tiny creatures can slip through. Forcing open the grate while fighting off the current requires a successful DC 30 Strength (
12c. Central Hub
The ceiling in this chamber forms a dome 40 feet higher than the floor around the cistern, which is 20 feet deep and fed by a submerged tunnel to the southeast. Water also pours in from 10-foot-deep troughs to the south and east, and forced westward and northward along troughs that lead to areas 12d and 12e, respectively.
12d. West Water Collector
The ceiling in this chamber forms a dome 20 feet higher than the floor around the cistern, which is 30 feet deep. Water pouring in from the east exits through a submerged tunnel in the north wall of the cistern, 20 feet below the water’s surface.
12e. North Water Collector
The ceiling in this chamber forms a dome 20 feet higher than the floor around the cistern, which is 40 feet deep. Water flowing in from the south and west exits through a submerged tunnel in the east wall of the cistern, 30 feet below the water’s surface.
Two dead grimlocks float in the cistern, with the brains torn out of their skulls. This is where the mind flayers dispose of creatures they feed on. Eventually, the corpses sink and get swept downriver.
12f. Dining Experience
The stone door to this room is soundproof, airtight, and sealed with a Qualith door lock (see “area Qualith Door Locks"). The ceiling is 10 feet high and flat. The room contains the following features:
Grimlock. A
stunned male grimlock is slumped in one of three stone chairs that face the door.Illithids. Two Mind Flayer are present. One stands behind the grimlock, feasting on its brain while telepathically communicating the experience to the second mind flayer, which looks on.
Dining on brains is a spectator event for mind flayers. With the aid of telepathy, the diner can convey the pleasures of a meal to other illithids in range. These mind flayers don’t like being outnumbered. They try to stun as many characters as possible, then gather reinforcements from area 12h.
Most of the grimlock’s brain is consumed by the time the characters arrive. Short of a
12g. Control Room
The stone door to this room is soundproof, airtight, and sealed with a Qualith door lock (see “area Qualith Door Locks"). The ceiling is 10 feet high and flat. The room contains the following features:
Extremiton. In the middle of the room, the ulitharid (see appendix A) sits on a swiveling crystal throne shaped like a cocoon. The throne’s base is shaped from a dark, alien metal. Dozens of thick copper wires connect it to plates of a similar metal bolted to the floor.
Crystal Screen. When the characters first arrive, the throne faces the room’s curved back wall, which has rows of pale white crystals embedded in it. These crystals project the flickering, spectral image of the Yawning Portal’s taproom, as seen through the eyes of its proprietor, Durnan.
Extractor Staff. A thin crystal stand near the throne holds a black metal staff shaped like a warped, alien spinal column. This is Extremiton’s extractor staff (see the “Ulitharid” entry in appendix A).
While seated in its crystal throne, Extremiton is psychically linked to the psipods in area areas 14 and area 15 and is maintaining its Waterdeep simulation (see “area Alterdeep"). If it leaves the throne, the simulation deactivates and the psipods shut down. When this happens, the mind flayers in area areas 14 and area 15 make their way here to find out why the ulitharid ended the simulation. It takes them 4 rounds to arrive.
Extremiton has enough on its mind without battling adventurers. If cornered here, it tries to negotiate a peaceful settlement. As a lawful evil creature, it tries to uphold its end of any agreement while twisting a badly worded deal to its advantage. Primarily, Extremiton is concerned with its own safety and the elimination of the githyanki. The welfare of the rest of the colony comes second. It places no value on prisoners and gladly releases them if doing so is enough to preserve its life.
The scene projected on the back wall is what Extremiton sees when it looks through the eyes of the virtual Durnan in the alternate version of Waterdeep. The view changes abruptly whenever the ulitharid switches characters in the simulation, and the scene fades entirely when the ulitharid leaves its throne.
Given a chance to do so, the ulitharid is delighted and eager to show off its Alterdeep simulation, which it is using to learn more about Waterdeep and its multifaceted culture. Extremiton fails to mention that once it becomes an elder brain, it plans to use its newfound knowledge to enslave the entire city.
12h. Ettin Thralls
This curved chamber has a flat ceiling 10 feet high. Lurking in the dark, empty alcoves to the north and south are four scrawny Ettin. At full health, each ettin has 60 hit points.
The ettins' minds have been broken by
13. Back Door
The double doors to these rooms are airtight, soundproof, made of stone, and sealed with Qualith door locks (see “area Qualith Door Locks"). Unless they are held open, the doors automatically close and lock. The ceiling here is 10 feet high.
The mind flayers use this back door to their fortress as a means of escape, in case the colony is overrun by githyanki or other invaders.
13a. Treasury
Two chests carved from zurkhwood sit atop low stone tables against the west wall of this room.
Treasure
The chests contain treasure that the mind flayers use to bribe creatures they can’t devour or enslave. Each chest contains 800 pp. Characters who dig through the gold also find a pair of purple-tinted crystal spectacles with platinum frames (2,500 gp), a
13b. Outer Guard Post
The north wall of this empty, unfurnished room contains a secret door.
14. Psipod Nexus I
The doors to this room are made of stone and sealed with Qualith door locks (see “area Qualith Door Locks"). Unless they are held open, the doors automatically close and lock. The ceiling here is 10 feet high. The room contains the following features:
Psipods. Resting in iron brackets along the curved walls are fifteen coffin-sized bronze cylinders with lids of transparent crystal. Each capsule is tilted at a 45-degree angle, connected to metal floor panels with thick copper wires, and coated in a thin, slimy residue.
Illithids. Four Mind Flayer carrying dark sheets of metal resembling clipboards are inspecting the capsules, nine of which contain
unconscious humanoids.
The mind flayers are tasked with ensuring that the equipment in this room is functioning properly. They try to stun intruders and trap them inside empty psipods (see “Psipods” below). Their “clipboards” are thin sheets of metal with braille-like writing (Qualith) embossed on them. The mind flayers use their tentacles to interpret the writing, which provides technical schematics for the psipods. A
Psipods
A psipod is a magic device that connects the mind of an
Any creature that enters a psipod’s bronze cylinder must succeed on a DC 17 Constitution saving throw or fall
While in a psipod, an
A psipod shuts down if it is disabled or destroyed. To disable a psipod, a creature must disconnect three of the eight copper wires connecting it to the metal panels in the floor. The mind flayers' schematic pads identify which three wires to disconnect on each psipod. (The combination of wires varies from one psipod to another.) If wires are torn out at random, roll a
All the psipods shut down if the ulitharid dies or leaves the crystal throne in area 12g. Each psipod is a Large object with AC 15, 50 hit points, and immunity to poison and psychic damage. A creature inside a psipod has total cover against attacks originating from outside the capsule.
Alterdeep
Unconscious creatures in psipods experience the equivalent of a shared dream as they appear with all their carried possessions in Waterdeep—or rather, an alternate version of Waterdeep created by Extremiton.
Through extensive telepathic contact with Waterdavians, the ulitharid has created a realistic simulation of Waterdeep that is constantly being refined for greater authenticity. Within “Alterdeep,” the ulitharid takes on various personas and quietly observes how creatures that are projected into the setting by the psipods interact with each other and the fake creatures and objects around them.
Alterdeep looks, sounds, smells, and feels like Waterdeep. Prolonged exposure to this alternate world, however, increases the possibility of detecting a flaw that betrays its true nature. Although Extremiton has created an impressive facsimile, characters who are drawn into the environment notice slight discrepancies in the way familiar NPCs act, or pick up on minor details that the ulitharid has gotten wrong or can’t reasonably duplicate: slight changes in decor, books that are blank between the covers, foul-tasting elven wine, dwarves unable to speak Dwarvish, and so on.
As soon as a character encounters such a discrepancy, the ulitharid also becomes aware of it, since their minds are linked. When confronted with an error, Extremiton either takes steps to correct it or tries to draw attention away from it. For example, it doesn’t know Dwarvish well enough to cause the residents of Alterdeep to speak it fluently, so it might subtly remove all known Dwarvish-speaking characters from the simulation until its familiarity with that language improves significantly.
The Yawning Portal: The most accurate and fleshed-out location in Alterdeep is the Yawning Portal. Extremiton is particularly fascinated with the establishment, its owner, and its clientele. Most newcomers to the simulation awaken here, and Extremiton tries to create enough situations of interest in the tavern to keep its captive audience engaged. Extremiton appears in the Yawning Portal as its gruff proprietor, Durnan, though it can inhabit other fake NPCs as well. The ulitharid has focused most of its attention on the Yawning Portal because that location sits atop the entrance to Undermountain and is a hotbed of humanoid interaction.
Damage, Death, and Healing: Creatures can be hurt, healed, and killed in the simulation just as they can be in the real world, and a character reduced to 0 hit points makes death saving throws as normal. Any creature that joins the simulation by entering a psipod and dies in the simulation also dies for real from the shock, as though it had taken enough psychic damage to instantly kill it. Creatures immune to psychic damage can’t be killed by this kind of system shock and stabilize automatically inside the simulation.
Leaving Alterdeep: If characters in the simulation try to escape Alterdeep’s city limits, Extremiton creates situations to dissuade them: bad weather, a city-wide lockdown, a festival—whatever it takes. The ulitharid hasn’t researched areas outlying the city. Consequently, nothing but thick fog lies beyond the city gates. The same is true for Alterdeep’s version of Undermountain; characters who descend the well in the Yawning Portal taproom find themselves enshrouded in fog with nowhere to go but back up. Extremiton, in the guise of Durnan, discourages exploration of Undermountain by claiming that the Mad Mage has magically sealed it off. Characters who are brought into the simulation can escape only if Extremiton allows it or if their psipods are shut down. The ulitharid might remove one or more characters from the simulation if it finds them too disruptive, in which case they’re taken out of their psipods and confined to area 10 until they can be fed to the neothelid in area 8. The characters can also try to form an alliance with the ulitharid. Extremiton might release them if, in exchange, they promise to destroy the githyanki that are threatening the mind flayer colony. You can roleplay these interactions or have the characters make ability checks to convince Extremiton to let them back into the real world.
Unconscious Humanoids
Eight of the humanoids in the psipods are Commoner of mixed race, alignment, and ethnicity. Their names are Daundarak Steelfist (LG male shield dwarf), Jarana Hammerstone (LG female shield dwarf), Falain Tlandrue (CG female moon elf), Merrily Shadowstep (NG female lightfoot halfling), Jagtar Uythrapp (LG male Mulan human), Lament (N male tiefling), Stormal Voss (LE male Illuskan human), and Lander Hellwind (CG male Illuskan human). All were abducted from Waterdeep. Apply racial traits to them as warranted, and remember that dwarves, elves, and tieflings have
The ninth humanoid is Selphorn Amcathra (NE male Tethyrian human noble). A resident of the town of Amphail, he was abducted after attending the funeral of a cousin in Waterdeep. Selphorn promises a reward of 500 gp for his safe return to the City of Splendors and makes good on his promise, but he puts his self-interest above all other concerns. Characters from Waterdeep would know that House Amcathra is one of the city’s wealthiest noble families.
15. Psipod Nexus II
This room is identical to area 14, with these alterations:
- The room contains twenty empty psipods in various stages of completion. (Half of the psipods are fully assembled and functional.)
- Three Mind Flayer are busily assembling one of the unfinished psipods.
16. Old Dwarven Halls
The doors in this area are made of stone and sealed with Qualith door locks (see “area Qualith Door Locks"). Unless they are held open, the doors automatically close and lock. Rooms here are 20 feet high with 10-foot-high corridors connecting them.
16a. North Guard Post
Scaladar. Two modified scaladar guard the hall. They are described in more detail below.
Furnishings. Water seeps into the hall through cracks in the arched, 20-foot-high ceiling, spilling onto a 40-foot-long stone table surrounded by stone chairs as big as thrones.
Dishware. Shallow niches in the walls hold stone dishes and tankards. Some of the dishware contains globs of edible gray slime. (The mind flayers use these dishes to bring food to prisoners in area area 10.)
Wall of Force. The rubble-strewn passage to area 8a is blocked by an
invisible wall of force that is generated from area 16c.
The mind flayers gained control of two scaladar (see appendix A) and implanted duergar brains in them, bestowing on each construct an Intelligence of 11 and the ability to understand (but not speak) Dwarvish and Undercommon. Each duergar brain is contained in a glass sphere embedded in the construct’s head. These scaladar obey the commands of illithids and attack any creatures that aren’t mind flayers or their thralls. Trobriand’s rings no longer have any effect on these constructs.
16b. South Guard Post
This misshapen, 20-foot-high room sits at the top of a sloped tunnel that descends for hundreds of feet to level 18. Guarding the otherwise empty room are eight duergar. If they see light approaching, the duergar turn
16c. Psionic Force Generator
Pedestal. In the middle of the room, two Mind Flayer grip the top of a 4-foot-tall, three-sided crystal pedestal with a fist-sized diamond floating 1 foot above it.
Anvils. Piled against the walls are scores of rusty iron anvils forged and abandoned long ago by the Melairkyn dwarves. (Each one weighs 500 pounds.)
The crystal pedestal with the diamond levitating above it is a psionic force generator, a magic device that allows the mind flayers to create and sustain the walls of force that enclose area 8. The mind flayers provide the mental energy that powers the generator. If these mind flayers are attacked, one maintains contact with the crystal pedestal while the other defends it.
The diamond no longer floats if removed from its place above the pedestal. A creature within reach of the diamond can use an action to take it. Without the diamond, the generator shuts down and the walls of force in area area 8 disappear. The device can’t function without the diamond (or another of the same or greater value). The walls of force also disappear if the mind flayers are pulled away from the pedestal—though the walls reappear if contact is reestablished, as long as the diamond is still floating in place. If the walls disappear, the neothelid in area 8 escapes in search of prey, killing and consuming any creatures it finds.
The crystal pedestal is embedded in the floor and can’t be knocked over, but it can be destroyed, rendering the generator irreparable. The pedestal is a Small object with AC 13, 20 hit points, and immunity to poison and psychic damage.
Treasure
The diamond is worth 5,000 gp.
17. Crumbling Bridge
Spanning the river at this point is a crumbling stone bridge that can support 200 pounds at a time. Any more weight causes it to collapse. A creature on the bridge when it collapses can leap to one side or the other with a successful DC 15 Dexterity saving throw. On a failed save, the creature falls in the river and might get swept away (see “area Underground River").
18. Gray Mold
The walls of this room are streaked with a slimy gray mold, some of which has been scraped off. Under the mold are bas-relief sculptures of dwarves chopping down large mushrooms.
The mold growing here is edible and nutritious, but not tasty. The mind flayers feed it to their prisoners. A small cup of the mold is nutritionally equivalent to a day’s worth of rations.
19. Unguarded Area
Neither the mind flayers nor their thralls come here.
19a. River’s Roar
Creatures in this 10-foot-high, partially collapsed chamber have disadvantage on Wisdom (
19b. Safe Shoreline Cave
The 10-foot-high, rough-hewn chamber is strewn with rubble. The shore is rocky and covered with loose dirt.
20. River Branches
The river (see “area Underground River") reaches a depth of 20 feet at this point, where it splits off in three directions. A creature swept along by the river’s strong current is pulled in a random direction determined by rolling a
Aftermath
If freed from its confinement, the neothelid wanders Seadeeps and consumes any other creature that crosses its path. Characters might try luring it to another level of Undermountain, where it can wreak even more havoc. If the neothelid becomes too great a nuisance, Halaster takes strides to either destroy or contain it.
Killing Extremiton completes a quest (see “area Uncover the Telepathic Spy"). Deprived of their leader, the surviving illithids disappear into other corners of Undermountain or return to the Underdark. With the illithids gone, the githyanki move to secure the level with reinforcements from level 16—assuming there are any githyanki left. If the githyanki are wiped out and Extremiton is allowed to live, it eventually turns itself into an elder brain, which attracts more illithids to the colony. In addition, the illithids continue to capture people from Waterdeep for their Alterdeep simulation, which grows more intricate and nuanced every day.