The Kimberley hole

The largest ever hand-dug excavation in the world, this 1097 meter deep mine yielded
over 3 tons of diamonds before closure.

Glory Hole, Monticello Dam, California

A  glory hole is used when a dam is at full capacity and water needs to be drained from the reservoir.  This one is the largest spillway of this type in the  world and consumes 14,400 cubic feet of water every second.

Great Blue Hole, Belize

This geographical phenomenon known as a blue hole is situated 60 miles off the mainland of Belize.