Earth's Belly Button!

Mir Diamond Mine located in Siberia, Russia  (Russian: Кимберлитовая алмазная трубка «Мир» Kimberlitovaya Almaznaya Trubka "Mir"; English: kimberlite diamond pipe "World" or "Peace"),  is the second largest man made hole on the earth being an open pit diamond mine.   It's about 1722 feet deep and about 3,900 feet in diameter.  The mine is so deep that it has caused the area to be a no fly zone for helicopters after a few were sucked down due to the downward air currents.  Today, the town of Mirny surrounds the hole with about 39,000 residents. 

The mine began in the 1950s and has been inactive for over 10 years due to low yields and safety concerns.  The area is about -40 degrees for 7 months a year making keeping machinery operating very difficult as rubber shattered, oil frozen and steel rigs would snap.  The the remaining months of the year the area was described as a sea of mud.  Even the building had to be build on steel pilings so they wouldn't sink into the sludge or permafrost.  During it's 50 years of operation, more than $17 billion worth of diamonds were excavated.