The largest hole in the world is a diamond mine in Mirny, Siberia – just below the Arctic Circle. According to Wikipedia, the mine is 525 meters (1,722 ft) deep (4th in the world) and has a diameter of 1,200 m (3,900 ft).
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From the BBC:
The town was founded in 1955 when geologists came to exploit the area’s substantial mineral wealth. The town is strictly off limits to outsiders without a special permit and the authorities regard any foreigners with considerable suspicion. The Mir mine was the first and the largest diamond mine in the Soviet Union.Its surface operation lasted 44 years, finally closing in June 2001.
 For more info checkout:
http://en.wikipedia.org/wiki/Mir_mine
