Type: Megadungeon
Region: Beneath Waterdeep
Known Levels: Dozens, though no accurate count exists
Creator: Halaster Blackcloak
Primary Inhabitants: Monsters, Underdark factions, adventurers, cults, magical entities
Known For: Endless dungeon levels, magical instability, deadly traps, ancient ruins, madness
Access Points: Primarily through the Yawning Portal in Waterdeep
Connected Locations: Skullport, Underdark tunnel systems, forgotten dwarven halls
Undermountain is the largest and most infamous dungeon complex in all Faerûn, sprawling for miles beneath Waterdeep through ancient caverns, buried kingdoms, forgotten ruins, magical laboratories, and impossible corridors shaped by centuries of madness and arcane experimentation.
To most people, Undermountain is simply called:
The Dungeon Below.
Countless adventurers have descended into its depths seeking:
Most never return.
The deeper one travels, the more unstable and alien the dungeon becomes. Entire civilizations have risen and fallen beneath the city, leaving behind shattered halls, cursed ruins, flooded caverns, and things best left forgotten.
Undermountain is inseparably tied to the mad archmage Halaster Blackcloak, whose influence still permeates the dungeon.
Once a brilliant wizard, Halaster’s mind fractured over centuries spent beneath the earth surrounded by immense magical power and isolation. His presence twists the dungeon constantly, reshaping halls, altering rooms, creating monsters, and warping reality itself.
Some claim Halaster is dead.
Others insist he still watches every descent.
Within Undermountain, the laws of logic and stability are unreliable.
Undermountain is not a single dungeon but an enormous labyrinthine network of:
Entire levels differ wildly in:
Some sections resemble abandoned cities.
Others feel almost alive.
Ancient dwarven halls connected to the Melairkyn kingdom still exist in portions of the dungeon, though many have collapsed, flooded, or become occupied by hostile creatures over the centuries.
Despite its dangers, Undermountain supports a strange economy built around adventuring and survival.
A constant flow of:
moves between Waterdeep, Skullport, and the dungeon itself.
Recovered goods include:
Entire businesses in Waterdeep profit from supplying expeditions descending below.
The most famous entrance to Undermountain lies within the The Yawning Portal, a tavern built around a massive shaft descending directly into the dungeon.
For many adventurers, the descent through the Portal marks the beginning of either fortune or death.
The tavern itself has become legendary as a gathering place for:
Connected to the upper reaches of Undermountain is Skullport, the infamous underground port city hidden beneath Waterdeep.
Smugglers, criminals, Underdark traders, mercenary companies, and desperate survivors use Skullport as a staging ground before venturing deeper into the dungeon.
Many expeditions resupply there before continuing their descent.
No single force controls Undermountain.
Different levels are occupied by:
Territories shift constantly through violence, magical disasters, and Halaster’s unpredictable influence.
Magic behaves strangely within Undermountain.
Arcane corruption, unstable enchantments, magical dead zones, living spells, and warped reality become increasingly common deeper within the dungeon.
Entire sections may:
Veteran adventurers quickly learn that maps are only partially reliable.
The upper levels of Undermountain are dangerous enough to kill inexperienced adventurers quickly.
The deeper halls are something far worse.
Ancient horrors, forgotten civilizations, elder creatures, magical catastrophes, and realms barely connected to reality itself wait below. Many who survive the upper dungeon eventually discover that Undermountain is less a constructed place and more a living wound beneath the world.
Some believe there is no true bottom.
Over time, Undermountain has created its own culture among those who survive it.
Veteran delvers speak of levels, factions, creatures, and routes with the familiarity of sailors discussing oceans. Rivalries form between adventuring companies, while taverns in Waterdeep fill with rumors, maps, warnings, and exaggerated stories from below.
Among experienced adventurers, surviving Undermountain earns respect few other accomplishments can match.