Monster Room

Dungeons were introduced in the Secret Friday Update 2. They are small rooms made of Cobblestone and Mossy Cobblestone (this is the only place that this block can be found in the game, so it might be wise to loot it). They are sometimes connected to caves, which leave an opening into the dungeon.

Dungeons usually contain a Mob Spawner and one or two Chests. The Mob Spawner acts as a guard against the loot. The chest contains treasure- Saddles, Iron ingots, Records, Buckets, Bread and String are a few things often found. It is possible to find a Dungeon outside, but this is very rare.

Dungeons can quickly be located using a map viewer. Set the viewer to show only cobblestone, and locate cobblestone that you did not place. Head out to one such place, and dig down until the Dungeon is found.

Dungeons seem to be able to spawn anywhere on the map. One user reported finding one under 3 blocks of sand, right next to his spawn point. Another user (underdog5004) found a dungeon above ground, in the side of a hill.

Dungeon Game Mode
Dungeon may be an upcoming game mode planned by Notch. Not much is known about it, but it will be like Survival mode. The player won't build blocks, only destroy some of them. It has also been said it will have new mobs and puzzles. It is planned to be released after the game.

See Adventure Mode.