Minecraft wiki entry for Stronghold, associated text: Strongholds vary in size. They contain several doors and rooms made mostly of stone bricks (45%), mossy stone bricks (30%), cracked stone bricks (20%) and infested stone bricks (5%). Infested cracked stone bricks and infested mossy stone bricks do not generate, unless silverfish enter these blocks.[1] Strongholds are lit by enough torches to provide visibility in most areas, though not enough to suppress mob spawns. Stairs that generate within these structures include stone brick and cobblestone stairs, but not their mossy variants.[2]