Lost Level

The Lost Level made up the sixth level of Undermountain. It was physically cut off for most of Undermountain's history, but umber hulks tunneled in, thus making the level accessible. Originally a temple complex dedicated to Dumathoin, it also held the tomb of King Melair.

Exits
The following ways could be used to leave the Lost Level:
 * A tunnel in the north part of this level led to level 5, Wyllowwood.
 * A tunnel in the southeast part of this level led to level 7, Maddgoth's Castle.
 * An archgate to level 9, Dweomercore.
 * A mirror gate to level 10, Murial's Gauntlet.
 * An archgate, in an empty room, to level 2, Arcane Chambers.
 * An archgate, embedded in an archway, to level 4, Twisted Caverns.
 * An archgate, in an empty room, to level 8, Slitherswamp.
 * An archgate to level 3, Sargauth Level.
 * An archgate to level 13, Trobriand's Graveyard.
 * In the same room as the gate above, an archgate to level 18, Vanrakdoom.
 * An archgate to level 5, Wyllowwood.

Inhabitants

 * Duergar: A duergar clan—namely, Clan Ironeye—were plundering this level of Undermountain circa 1493 DR.
 * Umber Hulks: Umber hulks burrowed into this level and wandered freely in search of food.