Minecraft wiki entry for Creating_a_challenge_map, associated text: In a very long corridor/mine, put a block at head height and place a redstone torch on it. Connect it to a sticky piston just below a huge tower of gravel! When the player breaks the torch block, the piston will retract and the gravel will fall down! Alternatively, make a double NOT gate (see Tutorials/Basic logic gates)leading to a command block that teleports the player to a Funbox room! However, this can be bypassed with ender pearls, but you can solve this problem by putting bedrock on the bottom.