Waterdeep:Undermountain

Over a thousand years ago, the wizard Halaster Blackcloak journeyed from far away to what is now known as Mount Waterdeep. With seven apprentices at his side, he used his magic to summon mighty beings from other planes to build a wizard's tower to dwarf all other wizard's towers. He dug deep into the mountain, eventually reaching the Underhalls, a mithral mine abandoned by the Melairkyn clan dwarves, where drow and duergar had taken up residence.

Using his new underground Undermountain complex as a base of operations, Halaster collected strange and dangerous creatures from other planes and from distant lands with which he populated his dungeon. Undermountain became Halaster's obsession, and he spiraled into madness. Those of his apprentices who stayed by his side were not spared his fate.

Over time, Halaster's tower fell into disrepair and then into ruin, and then Waterdeep was constructed in the shadow of the mountain. The early settlers sent criminals into the depths of Undermountain as punishment, for none returned alive. None, that is, until the adventurer Durnan ventured into the Mad Mage's lair and returned with riches aplenty. He used his newfound wealth to destroy what remained of Halaster's tower and build an inn in its place.

A knot in the Weave

Main page: Knot in the Weave

Before Waterdeep, and before Halaster, the ancient elven city of Aelinthaldaar stood here, capital of the elven kingdom of Illefarn. When the elves left, they used powerful magics to erase all traces of their capital city. As a side effect of their casting, they created a knot in the Weave underneath the mountain.

This snarl sometimes causes madness to one degree or another in the minds of mortals, which usually manifests as an obsession with the mountain and what lies under it. Not all who dwell in Undermountain succumb to the madness caused by this tangle of magic, but any who spend a considerable time below the surface risk falling victim to it.

The Yawning Portal

Main page: Yawning Portal

The Yawning Portal inn was constructed on the site of Halaster Blackcloak's tower, and the well leading into Undermountain still remains as a centerpiece in the tavern floor. Durnan constructed the inn after his first foray into Undermountain, and runs the inn today.

Adventurers who hang around the Yawning Portal often find work venturing into Undermountain on errands for others.

Undermountain secrets

Main page: Undermountain Secrets

There are many secrets you can uncover about Undermountain. Some you can learn by just listening in on patrons in the Yawning Portal, while others you may need to discover within the dungeon of the Mad Mage itself.

Alterations to magic

• No spell other than wish can transport someone into or out of Undermountain, or to travel from one level to another. Entering and exiting must be done by more conventional means, and traveling between levels must be done via conventional means, or via the gates that Halaster has created for that purpose. Astral projection, teleport, plane shift, word of recall, and similar spells, when cast for this purpose, simply fail. Similarly, any spell which would banish a creature to another plane of existence will fail. Any properties of magic items, even artifacts, are subject to the same restrictions.
• Despite technically being a different plane, magic that transports a creature to the Border Ethereal, such as the etherealness spell, works as expected. However, any venture into the Border Ethereal that begins within Undermountain and attempts to end outside it will cause the creature to be pulled back into Undermountain. Similarly, entering the Border Ethereal outside Undermountain and attempting to leave it within the dungeon will cause the creature to be ejected.
• Magic that summons creatures or objects from other planes works normally within Undermountain, as does magic dealing with extradimensional spaces. Any spells cast within an extradimensional space (eg, magnificent mansion) that was accessed from within Undermountain is subject to all of the same restrictions as spells cast within Undermountain.
• Spells cannot destroy or alter the shape of Undermountain's magically protected ceilings, walls, floors, pillars, or columns. For example, earthquake would not trigger a ceiling collapse or create fissures in Undermountain. Doors and furnishings, however, are not protected in this way.
• Characters who receive spells from deities or otherworldly patrons continue to do so within Undermountain. Spells which contact beings from other planes function normally.

Levels

There are 23 levels of Undermountain. On the first level, near the stairs down to the second level, a mural on the wall shows an abstract depiction of each level:

Pressing the flaming skull next to level 3 results in a voice saying "Gate access to Skullport disabled."

Pressing the comet next to level 16 results in a voice saying "Gate access to Stardock from level 16 only."

Pressing the tower next to level 23 results in a voice saying "Gate access to Halaster’s Tower from level 23 only."

Randolph Vistar has been mapping the dungeon as you progress. His maps (and others you've found) are collected here for reference. (OOC: Click on an image of a hand-drawn map below to see multiple versions, as Draltcur has progressively improved the map over multiple sessions.)

01. Dungeon Level

The Dungeon Level is the most commonly visited floor by fledgling adventurers, and as such it is largely picked clear of loot, unfortunately. There used to be a gang of failed actors called the Undertakers, who would disguise themselves as vampires and extort tolls from adventurers, but they're dead by your hands. The Xanathar Guild maintained several outposts on this level, as well; you've wiped them out, at least for now. The Dungeon Level is well-traveled, and it is unlikely to stay empty for long.

A map liberated from the Triumphant Trust

02. Arcane Chambers

The Arcane Chambers are home to the bazaar run by the Rustbone goblin tribe, ruled by Yek the Tall who has obtained a magic item that has transformed him into a handsome human. Some of the Rustbone goblins have entreated you to return Yek to his rightful stature, but so far he remains as you met him. The Xanathar guild maintained several outposts on this level, as well; you've wiped them out, at least for now. A male drow named Rizzeryl leading a small gang of wererats on behalf of the Zhentarim assisted you, but with his job complete, he may not remain in the Arcane Chambers much longer.

A map obtained from Rizzeryl

A map liberated from the Triumphant Trust

03. Sargauth Level

The Sargauth Level is cut in twain by the Sargauth River, which creates a water route to Skullport. It was once called Stromkuhldur, a home of the Melairkyn clan of dwarves, but Stromkuhldur now lies in ruins. The territory was contested by the hobgoblin Legion of Azrok and the drow House Auvryndar, but you have wiped out the drow in the area.

A map obtained from the Fine Fellows of Daggerford

A map created with the help of Will and Oleander, mapmakers in Skullport

Skullport

Skullport, the Port of Shadows, sits on top of an ancient Netherese ruin. Several years ago, the Xanathar Guild took control of the town, but since you've restored sanity to the the ancient Netherese flameskulls, the Xanathar Guild will have trouble maintaining meaningful power.

Lower Skullport

Middle Skullport

Upper Skullport

04. Twisted Caverns

Drow from House Auvryndar and an aboleth both recently moved in to the Twisted Caverns. The aboleth killed or enslaved many of the level's inhabitants, before you killed it right back.

05. Wyllowwood

Wyllowood is ruled by the druid Wyllow. You rid her forest of a tribe of goblin werebats at her behest (women and children included), which gave you her blessing to leave her domain.

06. Lost Level

Invisible things were stalking you as you traversed the Melairkyn tomb, until you found the Heart of the Mountain.

07. Maddgoth's Castle

A tiny floating castle owned by an archmage serial killer hovers over a huge cavern shrinks people down when they approach it. Below, a family of stone giants lives, unaware of the castle's presence.

08. Slitherswamp

A hot and humid swamp, whose control is divided between the Blacktongue tribe of bullywugs, and a group of nagas called the Ssethian Scourges. The nagas kept control over a large group of thralls with the help of a magical rod; you slew the nagas and took their rod, but a naga cannot be permanently killed without the aid of wish.

09. Dweomercore

A school of magic run by Halaster.

10. Muiral's Gauntlet

A gate on this floor connects to the Dungeon Level. Muiral the Misshapen and his undead control the northern half of the floor, while the drow of House Auvryndar controlled the south (until you killed them).

11. Troglodyte Warrens

The drow kidnap troglodytes from here to make them slaves. Two drow houses are in conflict here, and two great predators are hunting them.

12. Maze Level

The drow house Freth had a stronghold here, called Spiderwatch Keep. The matriarch of the house, Erelal Freth, forced Sim into marrying her, believing that he is the real Halaster Blackcloak. You and Halaster disrupted the wedding, and Halaster kidnapped Erelal while you slew the remaining drow.

13. Trobriand's Graveyard

A construct called the "bore worm" grinds its way through this level and up to the Maze Level every few hours. The Graveyard is a massive desert.

14. Arcturiadoom

The suffix "-doom" means the lair of a lich. Arcturia is one of Halaster's original seven apprentices. She built a Weapon of Mass Disintegration, which Halaster challenged the Delusionals to disarm within 10 minutes.

15. Obstacle Course

The former lair of the Death Tyrant named Netherskull, now dead.

16. Crystal Labyrinth

A group of githyanki reside here.

Stardock

The map of the dungeon on the first floor has a button depicting a comet next to level 16, and pressing the button results in a voice declaring "Gate access to Stardock from level 16 only."

Also called "Crèche K'liir", Stardock serves as a place for githyanki to raise their young, since they cannot do so on the Astral Plane (where creatures don't age).

17. Seadeeps

An ultharid named Extremiton was running a simulated copy of Waterdeep here, before you killed it and destroyed its colony with the help of some githyanki and githzerai.

18. Vanrakdoom

Vanrakdoom is where Vanrak Moonstar and his Shar cultists fled to, and where Glyster the bronze dragon chased them, before Shar's magic transformed him into the shadow dragon Umbraxakar.

Vanrak eventually repented his evil ways, and now his ghost wanders the dungeon, eager to see his old friend restored.

23. ???

Halaster's Tower

The map of the dungeon on the first floor has a button depicting a tower underneath the Elder Rune of the Mad Mage next to level 23, and pressing the button results in a voice declaring "Gate access to Halaster's Tower from level 23 only."

Gates

Halaster has constructed a number of magic gates throughout the dungeon. Most gates permit travel from one floor of the dungeon to another, although some allow for ingress or egress from Undermountain.

Opening a gate requires a key, though "key" in this case can be more metaphorical; some keys are the casting of a specific spell, or performing some specific act. Legend lore or similar spells can reveal what the key for a gate is, if no other means of learning the information is available.

Gates typically stay open for 1 minute, although wish can force one to stay open for up to an hour. A gate cannot be opened if it is within the area of an antimagic field, though if such a field encompasses an open gate, it will stay open for its duration. Dispel magic has no effect on gates. A gate cannot be damaged or destroyed except by wish.

Known Gates

Name	Floor	Key	Connects to
Gate of the Elder Wand	Dungeon Level (L1)	Touch the gate with a magic wand with at least 1 charge remaining.	Muiral's Gauntlet (L10)
Gate of Raining Gold	Arcane Chambers (L2)	Deposit 1 gold coin. The coin is lost.	Twisted Caverns (L4)
Gate of the Graven Tree	Arcane Chambers (L2)	Touch the gate with a dead twig or branch.	Wyllowwood (L5)
Gate of the Rusted Maw	Arcane Chambers (L2)	Touch the gate with a nonmagical item made of ferrous metal. The item is reduced to powdered rust.	Lost Level (L6)
Gate of the Golden Wyrmling	Sargauth Level (L3)	Place a gemstone worth 100 gp or more in the dragon's mouth. The gem is lost.	Lost Level (L6)
Gate of the Moonlit Mountain Gate of the Sunlit Mountain	Twisted Caverns (L4)	Moon: Insert the unicorn statuette's horn into the hole in the moon symbol Sun: ???	Lost Level (L6)
Gate of the Dancing Dwarf	Wyllowood (L5)	Replicate the dance depicted in the carvings	Lost Level (L6)
Gate of the Floating Fiends	Lost Level (L6)	???	Dweomercore (L9)
Gate of the Blind Gazer	Lost Level (L6)	An invisible creature stands before the mirror.	???
Gate of the Amber Flagon	Lost Level (L6)	Pour a pint of liquid on the floor within 5 feet of the gate.	???
Gate of the Penitent Dwarf	Lost Level (L6)	Unlock the keyhole in the bas relief (DC 20 Thieves' Tools). Using the key will cause the key to disappear until the gate closes.	Slitherswamp (L8)
Gate of the Runic Palm	Lost Level (L6)	Cast mage hand and press it to the indentation in the keystone.	Troglodyte Warrens (L11)
Gate of Prancing Goblins	Lost Level (L6)	???	Trobriand's Graveyard (L13)
Gate of the Forbidden Lovers	Lost Level (L6)	???	Vanrakdoom (L18)
Gate of the Riddled Sky	Maddgoth's Castle (L7)	Speak the letter "O" aloud.	Dweomercore (L9)
Gate of Tuoyaw	Maddgoth's Castle (L7)	Speak "Way Out" while pointing at the gate.	Muiral's Gauntlet (L10)
Gate of Interwoven Gears	Slitherswamp (L8)	Press the popped-out gear into place. DC 15 Perception check to find.	Muiral's Gauntlet (L10)
Gate of the Crystal Crown	Slitherswamp (L8)	Stand within 5 feet of the gate while wearing King Melair's crystal crown.	Troglodyte Warrens (L11)
Gate of the Open Tome	Dweomercore (L9)	An open book is held within 5 feet of the gate, which then disintegrates.	Arcturiadoom (L14)
Gate of the Felled Explorers	Muiral's Gauntlet (L10)	???	???
Gate of Weeping Blood	Maze Level (L12)	???	???
Gate of the Raging Torch	???	Hold a lit torch within 5 feet of the gate.	Troglodyte Warrens (L11)
Gate of the Skeletal Minotaurs	Maze Level (L12)	???	???
Gate of the Three Crossbowmen	Arcturiadoom (L14)	Three creatures hold hands while standing within 5 feet	Seadeeps (L17)
Gate of the Six-Fingered Gauntlet	Obstacle Course (L15)	Touch the arch with a six-fingered gauntlet	Seadeeps (L17)
Gate of the Soaring Drakes	Obstacle Course (L15)	???	???

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.

Each Elder Rune has a beneficial (boon) and detrimental (bane) effect associated with it. The caster who inscribes the rune can choose which effect to apply when the rune is triggered, or have the effect be chosen at random.

		Anarath, the Elder Rune of Protection and Sacrifice Bane: 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: 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.
		Angras, the Elder Rune of War Bane: 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: When the target hits with an attack, the target can turn that hit into a critical hit, after which this boon effect ends.
		Halaster, the Elder Rune of the Mad Mage Bane: 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: 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.
		Korombos, the Elder Rune of Chaos Bane: ??? Boon: 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.
		Laebos, the Elder Rune of Fire Bane: ??? Boon: 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.
		Lammath, the Elder Rune of Security Bane: For the next 24 hours, the target can't gain advantage on attack rolls, ability checks, or saving throws. Boon: Once within the next 24 hours, the target can use its reaction to reduce the damage it takes from one source by 10d6.
		Nchasme, the Elder Rune of Decision Bane: 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: The target can cast augury as an action three times, requiring no components and with no chance of a random reading.
		Savaros, the Elder Rune of Goblinkind Bane: All nonmagical coins and gems on the target's person vanish. Boon: ???
		Ullathar, the Elder Rune of Passage Bane: ??? Boon: For the next 24 hours, the target gains the following benefits: The effects of the freedom of movement spell, and the ability to cast the knock spell at will, requiring no components.