Minecraft wiki entry for Creating_a_challenge_map, associated text: Put a hard question to solve with 3 answers. To do so, put 3 levers and 3 signs with answers. The correct answer will open a path for the player to pass. Others will throw lava into the room. Take advantage of the fact that dispensers with buckets can place lava, and then suck it back up. Or, if you wish for a fancier way to kill your hapless victims, you can always use command blocks to do cruel stuff, such as striking a player with a lightning bolt, or blow the player up with instantly detonating TNT. Here's the command: