Minecraft wiki entry for Dungeon, associated text: Dungeons are small rooms made of cobblestone and mossy cobblestone and contain a mob spawner and up to 2 chests. Finding a dungeon without a chest is unlikely but possible. Additionally, there is a rare chance of a dungeon being found without a spawner. Occasionally, a dungeon generates with its chests in such a way as to create a double chest. Dungeons generate with either a zombie (50% chance), skeleton (25% chance), or spider (25% chance) spawner. The 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). Each block of the floor has a 25% chance of being cobblestone and a 75% chance of being mossy cobblestone.