Undermountain

Undermountain: The Mad Mage’s Labyrinth

Overview
Undermountain sprawls beneath Waterdeep like a wound beneath skin—a labyrinth of carved caverns and twisted magic. It begins in the ruined halls of Halaster’s Hold and stretches into depths older than memory. It is both dungeon and domain, containment and contagion.

Origins and History

  • Dwarven Foundations (–1288 DR onwards)
    Shield-dwarf Melair discovered a rich mithral vein beneath Mount Waterdeep. His descendants, Clan Melairkyn, carved magnificent halls—the Underhalls of Melairbode. They traded mithral for elven enchantment, ensuring stability and longevity.

  • Drow Invasions (circa 34 DR onward)
    Dark elves and duergar pressed the dwarves downward. The dwarves retreated, the drow claimed the upper halls, renaming the complex Kyorlamshin. By 211 DR the clan vanished—presumed destroyed or driven out.

  • Halaster’s Claim (168 DR–309 DR)
    The wizard Halaster Blackcloak erected a tower and ramparts atop the Deepwater Plateau. Driven by obsession, he summoned horrors, carved deeper tunnels, and seized the Underhalls. His apprentices, the Seven, carved out domains; Halaster slaughtered or enslaved surviving drow. The halls became his toybox—experimentation, destruction, arcane theatre.

  • Encroachments and Emergence (658 DR–1302 DR)
    A secret portal linked Cormanthyr to Undermountain; the Guild of Naturalists trespassed. Halaster retaliated by abducting wizards. Centuries later, the city’s sewers breached the caverns. In 1302 DR, Waterdeep’s Lords—kingmakers and pragmatists—began exiling criminals into the dungeon. Durnan and Mirt delved in, returned filthy rich, and Durnan opened the Yawning Portal tavern in 1306 DR to channel adventurers into the depths.

  • Shifting Ground (1375 DR–Spellplague)
    Halaster’s death triggered an earthquake. The Spellplague reshaped underground corridors. Portals vanished, reformed, twisted—new levels emerged; old paths vanished.

Geography and Structure

Undermountain defies simplicity: eight official layers plus fourteen sublevels, each a different brand of peril.

  • Architecture: Stone halls, 10 feet wide, 16-foot ceilings, minimalist geometry. No railings, granite floors—the mold of dwarven precision engulfed by Halaster’s whim.

  • Magic and Atmosphere: Teleportation and divination largely fail. Dead zones exist—magic black holes born from Halaster’s experiments. Ventilation exists, but pockets of foul air linger. Temperature varies; deeper levels can feel warmer—volcanic whispers in stone.

Levels and Notable Zones

  • Dungeon/Temple/Tomb Level: Dark temples ruin-ridden, graves for forgotten lords. A common first stop for adventurers seeking what lurks below.

  • Arcane Chambers: Twisted labs filled with traps, mystical architectures, Doomgates, tombs of lords like Hund Hillgauntlet.

  • Sargauth Level: A mighty river flows here—the River Sargauth. Features include the shattered enigma of the Sargauth Enclave, Skullport’s entrance, Pit of Ghaunadaur, and the settlement of Stromkuhldur.

  • Twisted Caverns/Farms: Underground breadbasket watered by the river, complete with bizarre agriculture that defies definition.

  • Maze Level: Home to a dwarven hold, Kyorlamshin’s remnants, drow outposts, Umber Hulks, River Graymurk—the Maze of Madness.

  • Seadeeps: Interfaces with the Underdark beneath the Sea of Swords—portal to other terrors.

  • Caverns of Ooze: Slimy horrors feed the dungeon’s living gore, intelligences shaped in mucilage.

  • Terminus Level: The deepest mines and caverns; portals here feed Undermountain’s hungry maw with new terrors.

  • Mad Wizard’s Lair: Rumored to hold Halaster’s greatest hoard. Legends planted by the mage himself to lure fools.

  • Sublevels:

    • Sewers (surface entry).

    • Wyllowwood (an underground forest under a magical sky).

    • Maddgoth’s Castle (miniaturized floating lair).

    • Muiral’s Gauntlet, Troglodyte Warrens, Trobriand’s Graveyard, Obstacle Course, Arcturiadoom, the Crystal Labyrinth, Vanrakdoom, the Runestone Level, Shadowdusk Hold—each a unique trial, each a trap, each a bloodied stage.

Rulers, Denizens, and Populations

  • Halaster Blackcloak: The architect—the mad, relentless proprietor. His presence haunts every trap, spell, and shadow.

  • The Seven: His apprentices spread throughout, carving domains, mutating halls. Some perished; some linger as ghosts in architecture.

  • Drow, Duergar, Undead, Constructs, Oozes: Some survive in remote halls, twisted by time and dark sorcery.

  • Adventurers: Driven by gold, glory, vengeance—or sheer desperation; many vanish, a few return with legendary loot.

  • Criminals: Disposed by Waterdeep’s elite. Some carve survival; most become monsters themselves.

  • Underground Inhabitants: In places like Stromkuhldur or Skullport, human outcasts, cultists, and opportunists build fragile dominions beneath the city.