Starter mob XP farm

The oldest mob farm design in the game, rebuilt by Voltrox, and the most watched tutorial in the library. A dark cobblestone box over deep ocean with dirt spawning floors, carpet to keep spiders out, and a ladder shaft dropping everything to a small kill window over four hoppers. No redstone at all. Voltrox says himself it is one of the oldest farms that exists, and no original designer is named.

• Build it over deep ocean, not a river. Rivers and shallow water spawn nothing, and this is by far the most common reason people get no mobs.
• Play alone while it runs. If another player is on the server the mobs spawn near them instead, which several builders traced their empty farm to.
• Difficulty on hard and simulation distance at 4 chunks. Two of the most upvoted comments on the video are just those two settings.
• Spiders still get through the carpet for some builders, and on Bedrock swapping the carpet for slabs fixes it.
• Stack another five or six layers above the first to raise the rate.
• Do not build it out of wood. Lightning can set the tower alight, and spare stone like diorite and granite is what most builders use.