Undermountain

A Dungeon for 5th Level Characters

Dungeon History

More than one thousand years ago, the wizard Halaster Blackcloak journeyed from a distant land to the base of Mount Waterdeep, perhaps acceding to the whispered summons of providence. Some believe he hailed from the nearly forgotten empire known as the Cradlelands. In ages past, humanity spread from the Cradlelands across Faerûn, originating from what is now the Plains of Purple Dust, a wasteland birthed out of a conflict with the gods. Others give Halaster less ancient origins, placing him among the early wizards of Netheril, or asserting that he came from a southern nation long since buried by sand and time. Whatever his origin, scholars have recorded that Halaster brought with him seven apprentices to Mount Waterdeep.
With the Seven guarding his back, Halaster tapped into his immense power to summon beings from other planes of existence to help him build a wizard’s tower to dwarf all other wizard’s towers. But as the seasons wore on, the Seven saw less and less of their enigmatic master. Halaster continued to use fell creatures from distant planes for tunneling and other construction beneath his tower, and the wizard kept the nature of most of his underground dealings a secret from the Seven. Eventually, Halaster’s exploration broke into the Underhalls, a complex of tunnels and rooms built by the dwarves around a mithral mine beneath Mount Waterdeep. The architects of the Underhalls, the Melairkyn clan, had long ago been killed or dispersed, and warring duergar and drow had settled in the ruins. Halaster began a crusade against both the drow and the duergar, participating in wild hunts with extraplanar allies through the tunnels. The stubborn duergar dug in until the mithral was largely mined out; then they abandoned the Underhalls, leaving the drow to fight Halaster and his minions alone. The Mad Mage rounded up the remaining dark elves, trapping some of their souls for use in his dark magic, while twisting the bodies and enslaving the minds of others. Once he had wrung the drow of their usefulness, Halaster Blackcloak tunneled on, ever downward, indulging his inexplicable compulsion for delving deeper and deeper into the mountain.
Using his underground complex as a base of operations, Halaster traveled to other planes and distant lands, collecting strange and dangerous creatures to live as prisoners, servants, or guardians in Undermountain. Populating and defending the dungeon became an obsession. Over time, the mage’s preoccupation with Undermountain electrified his eccentricities and infused him with an air of unconcealable madness.
Halaster’s apprentices came and went. Some left only to return - inexplicably drawn down into Undermountain’s depths. Others remained by his side. As they began dedicating more attention to their private obsessions, madness settled into their souls as well.
During the years Halaster quested on other planes and sequestered himself in his tunnels, his magnificent tower and its surrounding walls fell into ruin. In time, the city now known as Waterdeep developed in the shadow of Mount Waterdeep and spread down to the harbor. As the city sprawled outward over the years, it came to surround the ruins of Halaster’s home. Undermountain was known to those early settlers, and they often sent criminals into its endless depths as punishment. So it was for many years, until an intrepid adventurer named Durnan delved into the labyrinth beneath the tower and returned alive, laden with riches and countless harrowing tales. Durnan used his new fortune to demolish the remnants of Halaster’s tower and built an inn over the well he had used to descend into Undermountain, and call it the Yawning Portal. Durnan owns and operates the inn and tavern to this day, serving patrons and inviting the brave and foolish alike to test their mettle in the Dungeon of the Mad Mage.
Where Waterdeep stands today, there once stood Aelinthaldaar, the capital city of the ancient elven kingdom of Illefarn. When the elves left, they used a powerful spell to erase all traces of their capital. This spell had the unintended side effect of creating a permanent knot in the Weave, the fabric through which all magic is channeled. This knot lies deep underground and isn’t something that can be seen, felt, or undone, but it can cause madness to bloom in the minds of mortal beings who dwell near it for too long. The knot permeates Undermountain, and the madness it causes typically manifests as an obsession with the dungeon itself. Those affected by the knot in the Weave exhibit a subconscious desire to remain in or near the dungeon. Halaster and several of his apprentices fell prey to this obsession, as did many Melairkyn dwarves and Durnan, the proprietor of the Yawning Portal. Not all creatures that dwell in Undermountain succumb to its madness, and those who do aren’t even aware that the dungeon has them in its clutches.

The Yawning Portal

The Yawning Portal, a famous inn and tavern located near the eastern slope of Mount Waterdeep, derives its name from a 40-foot-diameter well that descends into the first level of Undermountain. Located in the center of the taproom, the well was once the outer shell of Halaster’s mighty tower, which was demolished long ago. Its sheer walls are made of old mortared stones. Next to this gaping orifice hangs a winch with a simple rope-and-pulley mechanism that Durnan, the proprietor, uses to lower adventurers down the shaft and (sometimes) pull them up again. Durnan controls the winch himself and will transport only one adventurer at a time. The trip takes 10 rounds, down and up. The rope is stained with old blood and long enough to reach all the way to the floor of the dark room at the bottom of the 140-foot shaft (level 1, area 1).
Durnan charges adventurers 1 dragon each to descend into the well, whether they opt to use the rope or not. The return trip also costs a piece of gold, sent up in a bucket in advance. He also readily accepts coin from patrons who want to place grisly bets on adventurers who dare explore Undermountain, and their odds of returning alive. “Five gold dragons says they’re back before a tenday, minus the fighter, the wizard, and the cleric!” is the flavor of commentary often heard amid gales of drunken laughter.
The walls of the well are crumbly but have abundant handholds and footholds. They can be scaled without climbing gear with a successful DC 15 Strength (Athletics) check. No check is needed to enter Undermountain by using the rope-and-pulley system.

Undermountain Secrets

Anyone who spends at least four hours in the Yawning Portal is likely to overhear tall tales about Halaster and his dungeon. Not all rumors are to be believed, however, and adventurers need keen ears and sharp insight to determine which stories have weight. Anyone who succeeds on a DC 20 Intelligence (Investigation) check or Wisdom (Insight) check learns a secret about Undermountain. Roll a d20 to determine which secret they discover, re-rolling on a 19 or 20.

1. Guild of Many Eyes

A thieves' guild that was driven from Waterdeep long ago still lurks in Undermountain, waiting and scheming to win back power in the city above. These villains make the sewers unsafe for honest folk to venture into. They have recently taken over Skullport, a subterranean town connected to Undermountain.

2. Immortal Insanity

The Mad Mage of Undermountain has destroyed himself or been destroyed many times, but his demise is always short-lived. Folk say the dungeon cannot exist without him, and so it magically re-creates the archmage whenever he meets his end within its crumbling halls. Each time Halaster returns, less of his sanity remains.

3. Skullport

Skullport overlooks the Sargauth River, a watery thoroughfare that cuts through the third level of Undermountain. Pirates once used the subterranean settlement as a trade port, but now it's a monster-infested haunt where spies and assassins hone their craft. Beware the fortress overlooking the river! Its garrison is commanded by an evil knight with a wyvern mount.

4. Tangled Web

Secret temples exist in great numbers in Undermountain, particularly those of evil gods not welcomed in the city above. The vile servants of these deities are locked in an endless war for supremacy in the dark dungeon. Lolth, the Demon Queen of Spiders, is the fiendish mastermind behind many of these bloody conflicts.

5. Arcturiadoom

One of Halaster's apprentices was a human transmuter named Arcturia, who created all manner of new monsters and often made herself the subject of her own horrid magical transformations. She claimed an entire level of Undermountain as her lair and polymorphed prisoners into monsters to guard it. It's likely that Arcturia resides in Undermountain still, in one form or another.

6. What Drow Fear

Part of Undermountain was carved out by the drow. Muiral, said to be a former bodyguard and apprentice of Halaster's, claims this domain and hunts trespassers for sport. These halls are littered with the bones of the slaughtered. Even the dark elves speak of Muiral in hushed tones. Anyone who can terrify the drow should be avoided at all costs.

7. Dwarfcraft

Much of Undermountain was built long ago by the shield dwarves of the Melairkyn clan. These dwarves were masters of stonework and hid many of their rooms behind secret doors. They also dug deep in search of precious metals. These mines were later stripped by duergar invaders, leaving a maze of worthless tunnels and caverns for monsters to inhabit.

8. School of Magic

Rumor has it that a wizards' academy has opened on one of Undermountain's levels. It's not known who runs this academy - perhaps one of Halaster's apprentices or the Mad Mage himself - but many mages have been drawn down to it. What wizard wouldn't want to glimpse the powerful magic gathering dust in the depths of Undermountain?

9. Mad House

The Shadowdusks were a Waterdavian noble family whose quest for political supremacy ended centuries ago after Shadowdusk wizards opened portals to the Far Realm. Twisted by madness and driven from their home, they sought assistance from Halaster and sank into the depths of Undermountain, never to be seen again - yet remnants of the noble house undoubtedly remain.

10. Underground Forest

The River of the Depths connects the fourth and fifth levels of Undermountain, skirting the edges of vast caverns filled with trees, shrubs, birds, other animals, and sunlight. An entire forest, as real as any found on the surface, waits to be explored, but an archdruid protects it. And explorers traveling downriver have seen a huge green dragon as well, perched on a tower near a bridge that spans the river.

11. Scavenger

The Sea of Swords has borne its share of pirate ships, none stranger than the Scavenger. This vessel could travel below the waves and through the air. No one has seen it in years. Perhaps it sank or was lost in the starry maelstrom of the night sky, but divination spells suggest it found its way into Undermountain. Others have searched for it below Waterdeep, but no one has found it and lived to tell the tale.

12. Trobriand's Army

Trobriand was one of Halaster's most promising and demented apprentices. Fascinated by machines, he carved out a level of the Mad Mage's dungeon for himself and set to work building an army of constructs there. It is said that Trobriand controls his creations with a metal ring, and that he crafted similar rings of lesser power for his apprentices, to protect them in the event that his constructs went insane.

13. Death Tyrant

Halaster has transformed an entire level of Undermountain into a proving ground for adventurers who seek to reach the deepest layers of the dungeon and the treasures hidden within. At the end of this underground obstacle course waits the greatest challenge of all: Netherskull, a death tyrant that hates wizards above all.

14. Nester's Fate

Halaster brought seven apprentices with him to Undermountain. One of them, Nester, attempted to become a lich using spells and methods of his own devising. But his process was flawed, and over time Nester's phylactery and body disintegrated until only his floating skull and skeletal arms remained. Driven mad by his failure to achieve true lichdom, Nester continues to haunt Undermountain in this weakened form.

15. Dark Elf Menace

Recent conflicts in Menzoberranzan have left weakened drow houses fearing for their future. Drow are coming to Undermountain in droves to carve out sanctuaries for one house or another. Halaster can't be happy to see them return in force, but who knows? Maybe the Mad Mage orchestrated the upheaval to bring the dark elves scurrying back for reasons beyond the comprehension of the sane.

16. Emerald Blade

Waterdeep was erected atop the bones of a dwarven kingdom built on the dust of a much older elven kingdom. It is said that a relic of the elves still waits to be found in Undermountain: a magic sword so sharp that its edge can slice through stone. Many adventurers have vanished during their hunt for the weapon, which, it is said, the elves blessed with the heart of a warrior and the soul of a poet.

17. Gith Who's Coming to Dinner?

Githyanki have invaded Undermountain. Perhaps they seek to destroy a mind flayer colony hidden in the depths of the dungeon, or perhaps they are planning to attack and plunder Waterdeep. There's one other possibility: the githyanki might be building a stronghold away from the timeless Astral Plane where they can raise their young and train them in the art of war.

18. Spire and Snail

Deep within Undermountain is a vast cavern containing a giant stalagmite that has been hollowed out to serve as a wizard's tower, perhaps even a refuge for the Mad Mage himself. The tower is guarded by stone constructs. No one knows what dwells inside. Not far from this tower lurks a most peculiar creature: a flail snail with a very valuable multihued shell.

Jhesiyra Kestellharp

Among the greatest of Undermountain’s secrets is the story of Jhesiyra Kestellharp, who was one of Halaster’s most gifted apprentices until it became clear to her that Halaster was irrevocably insane. She fled, but Halaster dragged her back to Undermountain and trapped her in the Citadel of the Bloody Hand, a dungeon complex under Mount Waterdeep connected to Undermountain. Jhesiyra escaped her prison when its wards failed during the Spellplague. To hide from Halaster, she magically confined herself in the stones of Undermountain. She now exists in a bodiless state, inhabiting the very dungeon itself. Halaster is unaware of Jhesiyra’s presence but also wonders over her disappearance following the Spellplague.
Jhesiyra’s plan is to use adventurers to defeat Halaster so that she can seize control of Undermountain. To that end, she does everything in her power to keep adventurers in Undermountain alive. Her abilities are, however, limited in her current, bodiless form.
Jhesiyra can exert control over Halaster’s magic gates, keeping adventurers from passing through them if she thinks they lack the might needed to defeat the perils beyond. Anyone who doesn’t qualify is pushed back without being harmed when trying to step through the open gate. Only a wish spell can allow someone to pass through.
Jhesiyra can’t stop adventurers from moving between dungeon levels by more conventional means. Whenever they enter a dungeon level that Jhesiyra thinks they don't survive, she sends them the following telepathic warning in Common: “Turn back! You’re not prepared for the danger that lies ahead!” Jhesiyra can’t and won’t elaborate on the nature of the danger that awaits the adventurers or communicate with them in any other way, for fear of being detected by Halaster.
Powerful divination magic can reveal Jhesiyra’s disembodied presence throughout Undermountain. But not even a wish spell or divine intervention will allow direct, two-way communication with Halaster’s former apprentice.

Elder Runes

Elder runes are ancient symbols imbued with magical power. With years of study, any creature that can cast the symbol spell can learn an elder rune and add it to the selection of symbols that can be created with the spell. Halaster has spent lifetimes studying elder runes, inventing new ones, and harnessing their volatile magic. He likes to place them throughout Undermountain as hazards. When an elder rune is encountered, roll a d10 to determine a random elder rune, re-rolling on a 10.
An elder rune is nearly invisible, requiring a successful DC 22 Intelligence (Investigation) check to find it. An elder rune has two possible effects: one beneficial (called the boon effect) and the other harmful (called the bane effect). A d20 is rolled to determine whether the bane effect (odd die roll) or the boon effect (even die roll) is triggered. A triggered elder rune targets one or more creatures within 60 feet of it, according to the caster’s specifications. Once the effect activates, the elder rune disappears and the spell ends.
A creature doesn’t make a saving throw against an elder rune’s boon effect. Saving throws made to resist the bane effect of Halaster’s elder rune have a spell save DC of 22.

1. Anarath, Elder Rune of Protection and Sacrifice

• Bane Effect: The target must succeed on a Constitution saving throw or it can't regain hit points until a remove curse or greater restoration spell is cast on it.
• Boon Effect: The target is immune to the blinded, charmed, deafened, frightened, paralyzed, petrified, poisoned, and stunned conditions. In addition, the target stabilizes immediately when it drops to 0 hit points. This boon effect lasts for 24 hours.

2. Angrad, Elder Rune of War

• Bane Effect: The target must succeed on a Constitution saving throw or it gains vulnerability to all damage and a -2 penalty to death saving throws for 24 hours.
• Boon Effect: When the target hits with an attack, the target can turn that hit into a critical hit, after which this boon effect ends.

3. Halaster, Elder Rune of the Mad Mage

• Bane Effect: The target must make a Constitution saving throw, taking 20d6 force damage on a failed save, or half as much damage on a successful one.
• Boon Effect: The target recovers its expended spell slots of 6th level and lower. If the target has no spell slots to recover, a magical shield surrounds the target for 1 hour instead. This shield grants the target resistance to all damage and can't be dispelled, though contact with an antimagic field destroys it.

4. Korombos, Elder Rune of Chaos

• Bane Effect: The target must succeed on a Wisdom saving throw or suffer the effect of a confusion spell with a duration of 1 minute.
• Boon Effect: When the target rolls damage, it can reroll any of the damage dice once. It must use the new rolls, after which this boon effect ends.

5. Laebos, Elder Rune of Fire

• Bane Effect: The target must make a Dexterity saving throw, taking 10d10 fire damage on a failed save, or half as much damage on a successful save.
• Boon Effect: The target gains a pool of ten d6s. Up to two of these dice can be expended at a time and added to any damage roll the target makes when it hits with a weapon attack. The damage added by these dice is fire damage.

6. Lammath, Elder Rune of Security

• Bane Effect: For the next 24 hours, the target can't gain advantage on attack rolls, ability checks, or saving throws.
• Boon Effect: Once within the next 24 hours, the target can use its reaction to reduce the damage it takes from one source by 10d6.

7. Nchasme, Elder Rune of Decision

• Bane Effect: The target must succeed on a Wisdom saving throw or be incapacitated for 1 hour. While incapacitated in this way, the target gains the following personality flaw, which supersedes any opposing flaw: "I fundamentally disagree with everything anyone else says."
• Boon Effect: The target can cast the augury spell as an action three times, requiring no components and with no chance of a random reading.

8. Savaros, Elder Rune of Goblinkind

• Bane Effect: All nonmagical coins and gems on the target's person vanish.
• Boon Effect: The rune magically summons a goblin, which appears in an unoccupied space within 20 feet of the target. The goblin is rude to everyone except the target and obeys the target's commands. The goblin vanishes in a puff of smoke if it drops to 0 hit points.

9. Ullathar, Elder Rune of Passage

• Bane Effect: The target must succeed on a Wisdom saving throw or be restrained for 24 hours.
• Boon Effect: For the next 24 hours, the target gains the effects of the freedom of movement spell and rhe ability to cast the knock spell at will, requiring no components

Dungeon Features

Common features of Undermountain are summarized here.

Regional Effects

When Halaster is in Undermountain, the following effects can occur in any location within the dungeon or in any extraplanar extension of the dungeon:

• A magical scrying sensor appears, taking the form of a ghostly, 1-foot-diameter humanoid eye surrounded by motes of light. The sensor is stationary, though Halaster can reorient the eye to face in any direction. Halaster can see through the eye as though he was in its space. The eye can’t be harmed or dispelled, but it winks out within an antimagic field. A scrying eye lasts until Halaster ends the effect (no action required).
• A minor illusory effect is triggered, as though Halaster had cast minor illusion in an area. Common illusions include the echo of rattling chains, the distant sound of explosive spells being cast, a dusty cloak or a rusty helm floating as though worn by an invisible figure, and illusory footprints appearing on a dusty floor.
• Silent apparitions of dead adventurers drift through halls and rooms as though they are lost. An apparition can’t be harmed, and it doesn’t acknowledge creatures or objects in any way. It can’t be dispelled but is suppressed within an antimagic field.

Alterations to Magic

Halaster doesn’t make it easy for creatures to enter or leave his dungeon. No spell other than wish can be used to enter Undermountain, leave it, or transport oneself from one level to another. Astral projection, teleport, plane shift, word of recall, and similar spells cast for these reasons simply fail, as do effects that banish a creature to another plane of existence. These restrictions apply to magic items and artifacts that have properties that transport or banish creatures to other planes as well. Magic that allows transit to the Border Ethereal, such as the etherealness spell, is the exception to this rule. A creature that enters the Border Ethereal from Undermountain is pulled back into the dungeon upon leaving that plane.
Magic that summons creatures or objects from other planes functions normally in Undermountain, as does magic that involves an extradimensional space. Any spells cast within such an extradimensional space (such as that created by a Mordenkainen’s magnificent mansion spell) are subject to the same restrictions as magic cast in Undermountain.
Spells can’t destroy or alter the shape of Undermountain’s magically protected ceilings, pillars, columns, walls, or floors. For example, an earthquake spell would not trigger a ceiling collapse or create fissures in Undermountain. Doors and furnishings, however, are not protected in this way.
While in Undermountain, anyone who receives spells from deities or otherworldly patrons continues to do so. In addition, spells that allow contact with beings from other planes function normally.

Sending Spells

Inside Undermountain, Halaster can’t be contacted by means of sending spells. Anyone that tries to contact him with a sending spell is magically redirected to the Mad Mage’s nothic secretary (level 9, area 31). Each time it is contacted in this manner, the nothic replies with a string of curses in Undercommon.

Architecture

Undermountain is made up of a mixture of smooth, worked stone and rough-hewn stone, with the occasional intruding natural tunnel or cavern. A few levels have exceptional architectural features; for example, level 16, the Crystal Labyrinth, has walls, floors, and ceilings made of crystal.

Ceilings

A room’s ceiling is at least as high as the room is wide, often higher. If a room’s ceiling height isn’t specified, assume it’s the minimum height.
A tunnel’s ceiling is as high as the tunnel is wide, unless otherwise noted. Most tunnels in Undermountain are arched and have no visible structural supports. Exceptions are called out.

Doors and Secret Doors

Normal doors (including double doors) are made of thick, sturdy wood fitted with iron hinges and handles, and protected against moisture by magic. Secret doors are fashioned of the same material as the surface in which they’re set (usually stone) and require a successful DC 20 Wisdom (Perception) check to locate, unless noted otherwise. When they are closed, most doors and secret doors create airtight seals, keeping gases and gaseous creatures from passing through them; exceptions are noted.
A one-way door can be manually opened only from one side (the other side has no handle or hinges). A knock spell or similar magic is needed to open a one-way door from the “wrong” side.
Not many doors in Undermountain have locks, but those that do sport locks of masterful craftsmanship. When confronted by a locked door, anyone with thieves’ tools can pick the lock with a successful DC 20 Dexterity (Thieves' Tools) check.
A locked or stuck door can be forced open with a successful DC 20 Strength (Athletics) check. A creature that fails a check to force open a door can’t make another attempt on the same door unless it has another creature or a tool (such as a crowbar) to assist.

Gates

Halaster creates magic gates that allow instant travel between levels of the dungeon. He can also create gates that lead into and out of Undermountain, which he uses primarily to restock the dungeon with monsters. His old gates were destroyed by the Spellplague, but Halaster has replaced them with new ones, most of which have destinations confined to the dungeon. These gates are not subject to the magic restrictions.
Opening a gate in Undermountain usually requires a special key, the casting of a spell, or some other act. Halaster likes to leave clues to help adventurers solve each gate. A legend lore spell or similar magic can also reveal the proper way to open a gate.
An open gate acts as a two-way portal and typically remains open for 1 minute upon activation. Creatures peering through the open gate can see the destination beyond as though they are looking through an open doorway into that location.
A gate can’t open within the area of an antimagic field spell or similar effect. Dispel magic has no effect on a gate, but a wish spell can permanently destroy a gate or force it open for up to 1 hour. A gate cannot be damaged or destroyed otherwise.

Arch Gate

This gate looks like an archway chiseled into a blank wall. The archway is 10 feet high and 10 feet wide unless otherwise noted. Most of the gates in Undermountain are arch gates.

Mirror Gate

This gate consists of a wall-mounted mirror, oval or rectangular, encased in a carved stone frame. The mirror is 10 feet tall and 5 feet wide unless otherwise noted. All the gates leading to and from level 10 are mirror gates.

Standing Gate

This gate forms between two standing stones or pillars. Unless otherwise noted, these columns are 15 feet tall and spaced 10 feet apart, with a stone lintel resting horizontally atop them to form a rectangular opening. Because the gate is freestanding, one can pass through it from either direction.

Elder Runes on Gates

When a gate opens, a random elder rune appears within its vertical plane. Halaster usually has the rune target the first creature that passes through the open gate. Once an elder rune is triggered, it vanishes until Halaster recasts the symbol spell on the gate.

Illumination

Since the creatures that originally carved out Undermountain had darkvision and Halaster lights his way by using magic, areas of the dungeon are unlit unless otherwise noted.

Type

Dungeon

Parent Location

Waterdeep

Included Locations

• Level 1: Dungeon Level
• Level 2: Arcane Chambers
• Level 3: Sargauth Level
• Level 4: Twisted Caverns

Characters in Location

• Halaster Blackcloak

Related Plots

• Dungeon of the Mad Mage