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Undermountain is a vast dungeon crawl under the area of Waterdeep in the fictional world of the Forgotten Realms campaign setting for the Dungeons & Dragons fantasy role-playing game. This dungeon has been used as an adventure setting for several computer games.
Undermountain was created by Ed Greenwood in 1975. It was the first dungeon for his fledgling Forgotten Realms campaign setting, and he used the Undermountain in both his Dungeons & Dragons and Advanced Dungeons & Dragons games.
The published campaign information originally described Undermountain as at least nine levels deep and possibly deeper. The majority of Undermountain was created and expanded from the natural caverns already in the area by a powerful and ancient wizard named Halaster Blackcloak, who dwelled in Undermountain and uses it as his personal playground and laboratory (307 DR–1370 DR).
The third level contains Skullport, also known as the Port of Shadows, and Qilué's Promenade of Eilistraee, a temple complex northeast of Skullport dedicated to the good-aligned followers of Eilistraee.
There are ruins of an ancient Ghaunadaur-worshiping drow city in a part of Undermountain near the Promenade whose inhabitants were single-handedly driven away by Halaster while he was creating Undermountain. The lower three levels were delved by dwarves. Below that not much campaign information is available. Madgoth's Castle also lies below the depths of Undermountain.
2018's Waterdeep: Dungeon of the Mad Mage describes Undermountain as 23 levels deep.
In 2003, Waterdeep and Undermountain served as part of the setting for the Neverwinter Nights computer role playing game expansion, Neverwinter Nights: Hordes of the Underdark, appearing in the first levels of the game.
Appearances and further reading
- Mark Anthony, Escape from Undermountain (Wizards of the Coast, 1996).
- Eric L. Boyd, Ed Greenwood, Christopher Lindsay, and Sean K. Reynolds, Expedition to Undermountain: Campaign Adventure (Wizards of the Coast, 2007). 
- Greenwood, Ed. Ruins of Undermountain boxed set (TSR 1060) ISBN 1-56076-061-3, Campaign Guide to Undermountain book page 3 (TSR, 1991)
- Erik Bethke, Game Development and Production (Wordware Publishing, Inc., 2003), 79.
- Padilla, Raymond (December 10, 2003). "Neverwinter Nights: Hordes of the Underdark". Game Spy. IGN Entertainment, Inc. Retrieved 2010-07-23.
- Hordes of the Underdark plot at Bioware official website