Mirny Diamond Mine - Eastern Siberia, Russia The world's second largest man-made hole, Mirny was constructed by Stalin to satisfy the Soviet Union's demand for industrial diamond. Further digging efforts were eventually abandoned when it became too diffic
The Great Blue Hole is a large submarine sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll 70 km from the mainland and Belize City. The hole is circular in shape, over 300 m across and 124 m deep.