Dungeons
From Hack/Mine Wiki
Dungeons are underground labyrinth-like structures. They consist of two coloured stone bricks. The primary block that surrounds the dungeon is unbreakable, so it is impossible to enter or exit from any location other than the specified entrance. There are a variety of rooms, which can range from jumping challenges with lava at the bottom, to a flat floored room with a small lava border. Inside each room, there is usually at least one mob spawner, sometimes two, and at most three. The mob spawners are random and are not always the same as any other in the room or in another room of the dungeon. Large Dungeons, like Super Towers, are dungeons with a much longer downward path which have more rooms and slightly better loot. As of v0.6, rooms to dungeons may be concealed by a brick which looks like the outer unbreakable brick but is breakable. Use the mini-map to help find the secret doors.
Levels
Dungeons have their own personal levels that are not the same as the level of the Area they reside in. These can be up to 4 levels higher than the Area's.