Inside Boulby Potash Mine

TEES DOCKS, UNITED KINGDOM - NOVEMBER 20: Workers walk alongside one of the storage silos at the potash facility at Tees Docks on November 20, 2014 in Tees Docks, United Kingdom. Cleveland Potash mine began production in 1973. At around 1400 metres deep it is the second deepest mine of this type in Europe and extends out to 7 km under the North Sea. Each year the mine produces over one million tons of potash and three quarters of a million tons of salt much of which is transported from the facility at Tees Docks. It operates 365 days a year and employs around a thousand workers. Potash products are used for fertilizer production as well as for glass making and applications in the chemical and pharmaceutical industries. The salt products also meet a variety of needs from winter road maintenance to sugar beet cultivation. (Photo by Ian Forsyth/Getty Images)