4. Diavik Mine – Canada:
The Diavik Diamond Mine is a diamond mine in the North Slave Region of the Northwest Territories, Canada, about 300 kilometres (190 mi) northeast of Yellowknife.
The mine is owned by a joint venture between the Rio Tinto (60%) and Dominion Diamond Corporation (40%), and is operated by Yellowknife-based Diavik Diamond Mines Inc., a subsidiary of Rio Tinto Group.
It produces 8 million carats (3,500 lb) of diamonds annually. The mine is so huge and the area so remote that it even has its own airport with a runway large enough to accommodate a boeing 737.
5. Sima Humboldt – Venezuela:
Sima Humboldt (Sima Mayor) is an enormous sinkhole located on the summit of the plateau of Sarisariñama tepui in Bolívar State, Venezuela.
The sinkhole was descended for the first time in 1974 and more thoroughly explored in 1976. Its volume is 18,000,000 m3 (640,000,000 cu ft), whereas the maximum width at its upper rim is 352 m (1,155 ft) and 502 m (1,647 ft) below.
Only 700 metres from the rim of Sima Humboldt there is another enormous sinkhole, Sima Martel. In total there are four caves on Sarisariñama.
6. Mirny Diamond Mine – Siberia:
The Mir mine also called the Mirny mine, is a former open pit diamond mine, now inactive, located in Mirny, Eastern Siberia, Russia. The mine is 525 meters (1,722 ft) deep (4th in the world) and has a diameter of 1,200 m (3,900 ft), and is one of the largest excavated holes in the world.
The airspace above the mine is closed for helicopters because of a few incidents in which they were sucked in by the downward air flow.