Minecraft wiki entry for Creating_a_challenge_map, associated text: Tripwires are a very good tool and plays a role in this trap. Place a tripwire, then wire it up to a set of pistons. Make sure that the tripwire hook is in a place where it's impossible or very difficult for the player to see it. When the player comes along, they will not see the tripwire, so they will trip over the wire, and stumble into a pit that you made beneath the pistons. Make it fall into a ravine, a funbox or, if you are really mean, an end portal.