Zombie free layered iron farm

A layered iron farm with 20 villagers per layer and no zombie in the design. The villagers spawn golems on their own, water carries them to the centre, and campfires kill them over the hoppers. Layers are added above to raise the output. Java only.

• The pit dimensions in the video do not match what is said. Builders end up with a 4x4 middle instead of 3x3, and the fix given is to dig 18x18 rather than 19x19. One commenter traced it to the build changing between cuts.
• Without a zombie the farm stops at night, because the villagers sleep. Sleep through the night yourself, or trap a zombie in view of each villager box to keep it running and raise the rate.
• Villagers that have already slept in a bed somewhere else will not claim the new beds. Break the old beds in your trading hall or breeder first.
• Golems spawn outside the pit unless the whole surrounding area is spawnproofed with path blocks. Bring a lot of shovels.
• A slab roof does not protect the villagers from lightning. One builder lost two to witch conversion and says the tutorial is incomplete without a lightning rod.
• Water is the step people get stuck on. Place the lower water buckets only on the third block either side of each fountain block, not on every block.