The standard layout is composed of two levels inhabited by rogues, minotaurs, jellies, and other assorted monsters. Each level is a maze consisting entirely of darkened two-wide corridors, with the entrance in the northwest corner, and the exit in the southeast corner. The walls are not diggable. The first level is very large, while the second is much smaller. In the southeast corner of the second level is a special exit that leads back to the surface.
The boss is the Minotaur of the Labyrinth, a minotaur with Berserker talents, and appears in a random location on the second level. Beware that the boss will immediately target the player and pursue them once they enter the level, so one needs to be prepared to engage the boss quickly.
Rogues will discover a special scroll of lore which will teach them how to make a poison gas trap.
This zone also has an alternate layout, with four slightly smaller floors. The orderly maze has been shattered, and you will find horrors in addition to the rogues and jellies. Each floor has multiple holes ("huge crack in the floor") that you can jump down to reach the next floor. There are no stairs to travel back up, so be sure you are done with the current level before taking the leap.
The boss in this alternate layout is the Horned Horror. It will also start hunting for the player as soon as they enter the level.