Minecraft wiki entry for Drowned_farming, associated text: This is a small room at the top of the drop shaft. The drowned fall into this room from the spawning platform above it. The purpose of this room is to create a measured distance for the drowned to fall, because the spawning platform is by necessity a lethal fall distance higher than the killing platform, and you don't want the drowned to die except by your own hand! So you must build a small platform covered with flowing water for the drowned to fall into safely, and be swept by the water into a 1×1 hole in the corner of the room, which is the top of your drop shaft.