SubTropolis, Kansas City is a 1,100-acre underground storage facility said to be the world’s biggest. It maintains a temperature of 18-21 degrees year round, which is why the US Postal Service keeps its collectible stamp collection here. There are also plans to farms mushrooms and store crude oil. Dug into the Bethany Falls limestone mine SubTropolis is at places 49 m beneath the surface. It has a grid of 4.9 m high, 12 m wide tunnels separated by 7.6 m square limestone pillars created by the room and pillar method of hard rock mining. The complex contains almost 11 km of illuminated, paved roads and several miles of railroad track. Currently 460,000 m² is occupied and 930,000 m² are “improved.” About 13,000 m2 of available space are added each year as active mining continues. Other facilities like SubTropolis exist although not on the same scale, such as the abandoned mine in Butler, Pennsylvania used by Corbis and the US Federal Government for secure storage. As the room and pillar mining method is used to extract limestone throughout the Midwest, many companies are looking at ways to utilize the hundreds of millions of square feet created in this manner for everything from mushroom farming to crude oil stockpiling.
