Minecraft wiki entry for Secret_door, associated text: Secret doors are concealed entrances into places created by the player. They are useful for a variety of things, such as protecting valuables on a multiplayer server, building a adventure map, or just for fun. Some hidden doors, such as piston doors, require a redstone opening mechanism to tell the door to open. This tutorial will attempt to cover the basics of a few different types of hidden doors. Note that some of the doors listed are well known so don't be surprised if someone spots it right away.