The Undermountain

Undermountain was once the site of Melairkyn, a dwarven stronghold built beneath Mount Waterdeep. When the dwarves were driven out, the Mad Mage Halaster Blackcloak descended into its depths, seeking solitude for his experiments.

What followed was centuries of arcane alteration, extraplanar grafting, and magical madness. Halaster reshaped Undermountain into a multi-layered dungeon city, populated by monsters, illusions, sentient traps, portals, and reflections of his fractured mind.

No one knows the full scope of Undermountain. Not even Halaster—if he still exists in a form we would recognize.

Undermountain is said to contain at least 23 named levels, each distinct in architecture, inhabitants, and theme. Known sections include:

• The Dungeon Level – The first floor, often reached from the Yawning Portal. Contains false paths, undead remnants, and shifting staircases.
  
• The Arcane Chambers – Laboratories, spellforges, and broken portals once used by Halaster’s apprentices.
  
• Skullport – A city-sized cavern of criminal activity, midway between Undermountain and the Underdark.
  
• The Twisted Caverns – Warped reality and inverted gravity. Time passes inconsistently here.
  
• The Deep Sea Mirror – A flooded level that reflects surface events incorrectly, showing distorted versions of current history.
  
• The Spell Tomb – A supposed vault of spell knowledge and forgotten Weave threads. Sought by many. Found by none.

Undermountain’s geography changes, resets, and reacts to intrusion. Some adventurers report different layouts on different visits. Others are never heard from again.

Undermountain is alive with threats, including but not limited to:

• Halaster Blackcloak – Believed to still exist in some arcane form. Appears rarely. His avatars are unpredictable, cruel, and sometimes helpful—if only to cause chaos.
  
• Mad Constructs – Golems, homunculi, arcane weapons, and mirror-born duplicates.
  
• Beholder Outposts – Remnants of The Xanathar Guild, pushed deeper underground by the events of The Grand Game.
  
• Dead Three Cultists – Banite, Bhaalite, and Myrkulyte faithful seeking ascension through madness.
  
• The Pale Choir – A rumored chorus of ghosts that sings spells backward, unraveling reality.
  
• Portals to Elsewhere – Undermountain is stitched with malfunctioning gateways to the Feywild, Shadowfell, and stranger realms.

During the Grand Game, Undermountain remained largely untouched, though several factions attempted to use its depths:

• The Hype Squad first entered Skullport via an Undermountain spill tunnel.
  
• The Unseen had at least one laboratory on the seventeenth-level, where they tested mind-control spores and psionic sigils. The Delta Wolves, a small thrown together adventuring party, fought their way out of captivity here facing off against Therlin Heskan
  
• Jarlaxle's agents used ancient portals to smuggle artifacts through Undermountain into Luskan.
  
• Rumors persist that one of the Eyes of Golorr was once hidden in Undermountain, but removed decades ago by a clone of Manshoon.

To this day, the City Watch and the Harpers do not patrol beneath the first level. There is no law in Undermountain—only daring, delirium, and death.

Among adventurers, Undermountain is the ultimate trial. To descend is to gamble with fate, to risk not only one’s life, but one’s soul and sanity. Among scholars, it is a focal point of arcane curiosity—a living lab experiment left untended.

Some say the dungeon grows stronger with each adventurer slain, feeding on ambition and arrogance. Others believe it is Halaster’s final joke: an eternal dungeon that watches the world change above, unmoved and unconquered.

I do not map Undermountain. Maps are lies in that place. I do not chronicle its levels. They do not stay level. I remember it only as one remembers a nightmare—poorly, and with scars.