What the hell is that humongous funnel west of the center.

I'm always amazed by the size of the constructions people make in Minecraft (without the use of external editors). Myself, I once undertook to dig a 16x16 hole to the bottom of the world and build a tower to the sky. Never again, that was way too much useless work.

Then again, this is multiplayer, so there's extra motivation of group effort.