With an expected value of £13billion, this could be the most expensive hole in the world. Dubbed 'Diamond City', Mir mine in eastern Siberia is so huge it creates a vortex potentially strong enough to suck helicopters into its depths. At 1,722-feet-deep and with a diameter of nearly one mile, the crater makes it look like the nearby town of Mirny has been struck by a meteorite. The air space above the pit, located 5,000 miles east of Moscow, is closed after alleged incidents of helicopters being sucked downwards. Thankfully, no crashes have been reported. It is owned by Russian company Alrosa, which produces about a quarter of the world's diamond output.