Monster Room

Dungeons are naturally generated structures that appear in the Overworld. They are small rooms made of Cobblestone and Moss Stone and contain a hostile Mob Spawner and up to 2 Chests. Finding a dungeon without a chest is very unlikely, but possible. Occasionally, a dungeon will spawn with its chests in such a way as to create a double chest. Dungeons generate with either a zombie, skeleton, or spider spawner that can easily be deactivated by placing torches all around the spawner.

Anyone exploring a cavern should be wary of encountering a dungeon, as they are almost always connected to large caverns. Also, a dungeon generated near the surface of a desert biome will cause sand to collapse and form a square depression. This can be a good way for inexperienced players to locate a dungeon and the resources associated with them.

Dungeons do exist on Peaceful mode, as they are generated with the map. Monster Spawners will still spawn mobs in peaceful mode, but the mobs will instantly despawn.

Properties
A perfectly generated Dungeon, one which has not been overwritten by other generated terrain, will:
 * Be 5x5, 5x7 or 7x7 of floor space in size
 * Have cobblestone walls, and a mix of cobblestone and moss stone floor
 * Have 0-2 chests
 * Have a hostile monster spawner (these can be easily utilized by the player for mob farming)

It is very likely for a dungeon to be overwritten by other generated terrain, thus distorting the dungeon. It is also possible, but rare, to find two dungeons joined together, with 2 spawners and 0-4 chests - although sometimes (even more rarely) triple dungeons can be found with 0-6 chests and 3 spawners.

The mob spawner acts as a guard for the loot, spawning an indefinite number of mobs until the player can light up the room sufficiently to stop new mobs from being spawned, or simply break the spawner itself. This is usually accomplished by placing a torch on or around the spawner. The mob spawner is always in the center of the dungeon room, with chests located around the walls of the room (large chests can connect with the short side against the wall). The chests contain randomly generated treasure that are placed in random slots.

The spawner type in the dungeon depends on the floor pattern(proved in panda4994's 20th survival video)

It is usually fairly easy to convert a dungeon to a "minifarm" for experience and drops, but the details will vary with the dungeon's location and environment. However, the spawner will not activate unless the player is standing within 15 blocks of it.(See Mob Spawner)

Chest contents
Each dungeon chest block contains up to 8 item stacks, with the following distribution:

This information was obtained from Minecraft's code. The generation algorithm places one of these items in a random slot in the chest eight times, possibly overwriting items already placed.

Locating a dungeon
Dungeons can generate almost anywhere underground, but they are most common around Layer 26, and frequent between Layers 16 and 42.

A reliable way of locating dungeons is through listening, either for a large amount of noise from one kind of mob, or for ambience. Neither of these things are an exclusive trait of a dungeon, but they do mean that there is an unlit and unexplored area nearby, which may well be a dungeon, particularly in the case of frequent, similar mob noises.

Some was to locate a dungeon include searching for moss stone inside of a cave and looking in abandoned mine shafts, as well as looking for cobblestone not placed by players (and not lava-related).

Another way to find a dungeon is to look for fallen sand or gravel in a square pattern.

Very rarely, dungeons will spawn in the side of a mountain making them easy to spot but hard to safely reach.

Video
''Note: This video was created before the release of. Since then, mossy cobblestone can be found in Jungle Temples (12w22a) and Mega Taiga biomes (13w36a).''

spawner type proof http://www.youtube.com/watch?v=9iaU1TvIQqM&list=SPOfxMC0BlfPKWoK03sjuP0H5Z-kepf5o5&index=20

Tips

 * To defeat a dungeon, aside from the obvious method of fighting the monsters and lighting up the area, one can instead tunnel underneath it and destroy the spawner from below.
 * It is also possible to dig a tunnel above the dungeon and flood the area with lava, kill all of the mobs, then place torches to disable the spawner just as the last of the lava disappears. You can fill the entire dungeon with sand and/ or gravel. When the blocks that gravity applies to fall on top of the mobs, they will be crushed and killed. Once the room is filled, you can dig out the chest and loot it. You can also set a block of TNT above the spawner and prime the TNT, but doing so will destroy the spawner, and the dungeon cannot be used as mob grinder.
 * Digging around the sides of the dungeon will allow you to bypass the spawner and loot the chests directly without any risk of health loss.
 * A fast way to collect loot from the chest is to destroy the chest rather than removing the items from it. This way you collect all loot as well as the chest.
 * Torches can be placed directly on the monster spawner. Placing one on each side provides the same effect as placing a torch on the blocks adjacent to the spawner, without needing to be replaced when you mine the floor out for Moss Stone.
 * The correct tool to break a spawner is a pickaxe. It will take a few seconds this way, vs 45 seconds or so with a sword.

Trivia



 * The spawner will drop 13-40 XP when broken by the player
 * Dungeons will still generate if the 'generate structures' option is toggled to off, even though they are claimed not to by the in-game description.
 * Dungeons are almost always connected to a cavern, and because the cavern can be as small as a single block of air, the dungeon could completely overwrite it, usually resulting in a dungeon with no entrance.
 * Rarely, a mushroom will appear in a dungeon on mossy cobblestone.
 * It is possible, though almost impossibly rare for a dungeon to be generated at bedrock level, thereby deleting the bedrock. In which case digging through the moss stone can lead into the Void.
 * Rarely, on peaceful, a monster spawner may spawn a monster that plays its sound file before it can despawn.
 * If a dungeon has fallen gravel or sand in it, then placing a torch on the spawner may not be sufficient to light up the entire area to prevent spawning.
 * It is rarely possible for a player to find a dungeon with two spawners and up to 4 chests. This only occurs when a 5x5 dungeon spawns within a 7x7 dungeon, since the dungeon will remove any blocks from the walls or floor that open into a cave, the walls of the smaller dungeon will be removed, resulting in a 7x7 floor space with one spawner in the middle, and a second spawner adjacent or diagonally adjacent to the first.
 * Double-chest dungeons as shown below may have chests that form a perpendicular barrier between the wall and spawner (an exception to this would be in 7x7 dungeons, in which the chest cannot reach the spawner):
 * Each block of the floor (including under the walls) has a 25% chance of being cobblestone, and a 75% chance of being moss stone.
 * If a dungeon loads in two chunks and one regenerates (often causing a flat vertical wall), the dungeon can become partially generated. This can be found if one of the walls of the dungeon is not cobblestone, but rather stone. Sometimes, the partially generated dungeon will not have a spawner or a chest. Example of a partially generated dungeon
 * The contents of chests in dungeons appear to be based on the world seed.
 * If you are playing on peaceful in a skeleton dungeon, sometimes skeletons will shoot arrows before despawning.
 * Many players consider skeleton dungeons as the hardest to conquer. However, an easy tactic to use is to let many (5-6 are recommended) skeletons to spawn. Then, simply run inside of the dungeon. Most of the skeletons will be in such a frenzy to hurt you that they will shoot each other, and eventually kill themselves. While they are doing this, spam torches on the walls, preventing further spawning. If you want, you can kill some of the skeletons on your own after you are finished with the torches. Armor (preferably iron at least) and a stone, iron, or diamond sword are recommended.
 * It's possible for a Nether Portal to go into a dungeon when leaving the Nether.
 * It's possible to get both types of record in the same dungeon chest.