Minecraft wiki entry for Door-based_iron_golem_farming, associated text: Before placing your doors, you should first complete the trap. To sweep the iron golems from the pit into the hole, it's best to cover the whole area with running water, otherwise the iron golems will try to stick to the dry spots. The design shown here has a 1 block undercut around the pit's edge, with water sources along two parallel sides, 2 water source blocks at the middle of the other two sides for the final sweep. This design uses lava blades across the top and middle of a 2-wide by 3-high tunnel leading from the hole. At the bottom of the hole is a river that sweeps the mobs into the blades, and sweeps the loot toward the end of the tunnel.