“1957, Stalin had ordered the Mirny diamond mine to be built, and construction was underway. If space and manpower allowed, this was to be the biggest and most successful diamond mine that the world had ever seen. However, the construction process presented a few problems. /…/
In 2004, it closed for good. Officials stated that there was a flood and that they had gone too deep to mine any further. However, conspiracy nuts and diamond dealers floated around alternative theories.
Now, the massive open-air hole of the Mirny diamond mine lies abandoned, though underground research into diamonds continues, conducted by Russian company Alrosa. The airspace above it is restricted, as the sheer depth of the mine can suck helicopters into it. When the cold air from the surface meets the heated air coming from the bowels of the mine, it creates a vortex powerful enough to suck helicopters and small aircraft down into its depths. Several incidents have been reported.
In 2010, Russian company AB Elise announced plans to build a giant, futuristic domed city within the mine which would provide solar-powered homes to over 10,000 residents. Though, so far no plans have been drawn up.
For now, the Mirny diamond mine remains a mysterious vortex, a seemingly-bottomless pit that once produced more than half of the world’s diamonds and transformed the Soviet Union from a war-torn republic to an international economic powerhouse.”
(www.allthatsinteresting.com)