Minecraft wiki entry for Secret_door, associated text: Using a hidden wooden pressure plate, an arrow can be fired at a predetermined location, activating a door. As arrows despawn after 1 minute, the secret doorway can close automatically. If this 1 minute period is too long, pressure plates can be added inside the door to close it prematurely. It can be difficult to hide a pressure plate. Some ideas include behind a waterfall, under a lava pool, or in a fake minefield.