Minecraft wiki entry for Stronghold, associated text: Strongholds feature various types of main rooms. Each room has an entrance, which is either a plain 3×3 opening, a wall with a wooden door, a wall with an iron door (with buttons), or a 3×3 opening with a gate of iron bars along the top and sides. Rooms may have exits to other room pieces or dead-end "exits" into stone. Additional "passages" between rooms may exist if their generation overlaps or if the stronghold intersects a cave, mineshaft, or other structure. Sometimes, doors can be sealed off by stone bricks, resulting in "secret doors", usually occurring with 5-way crossings.[3]