Minecraft wiki entry for Creating_a_challenge_map, associated text: Deathdome: Use MCedit or commands to make primed TNT spawners. Set them to 1 tick minimum and 20 ticks maximum. Set to 8 ticks as current time. Add a spawning range. Don't forget to cover the room with obsidian including the spawners or weep! When the players enter the room, hundreds of TNT will explode right into their faces! Add diamond armor for them.