Minecraft wiki entry for Spawner_traps, associated text: Dig one block north and two blocks south (three blocks tall for each direction), then go towards the south end, and make an access shaft. At the north end, dig a shaft, 30 blocks deep, and three pointing west. At the bottom, make a small room and light it up. Place ladders on the west end, and make an access shaft to the top of the ladders. Place blocks to the east of the ladders, except for the bottom few.