HydeCo. Knox Underground!

440 manholes open onto a sewer two levels deep: catwalks above, the channel below, side rooms with their own loot, and wall lamps that go dark at the power shutoff. Pry a cover up with a crowbar and climb down the ladder.

Eight dry wells hidden in the countryside drop into caves laid out by hand. Bring a rope to tie to the well.

Toggle mining mode and swing: a pickaxe breaks rock, a shovel digs down, a sledgehammer breaks into basements. The ground has layers down to bedrock, with coal, iron and copper seams in parts of the county.