The majority of the third level of the Upper Dungeons lies twenty five feet below the second level. Much of the eastern portion of the map is actually somewhat deeper than the rest of the level.
The walls and floors are generally made of rectangular stone blocks fitted together tightly, except as noted otherwise, and especially within the Chapel of the Worm beginning in Room 62, where the are decorated with a spiral design on a rough surface resembling stucco. Ceiling height is generally fourteen feet, and cressets are irregularly placed for holding torches.
Caves and cavern areas have sandy floors and ceiling height varies considerably, but is never less than seven feet.
Level 3 directly connects to Level 2 and Sub-Level 3A of the Upper Dungeons, the Twilight Dwarf holdings, and the sub-levels of the Red Keep (from Area 57). In addition there is an exit to the outside and the beginning of a great staircase that reaches much lower levels.
Several competing factions are present. The Bugbears lair in Rooms 36 to 55. Two separate groups of orcs are present, and a tribe of froglodytes inhabit portions of this level and Sub-Level 3A.