Michigan Natural Storage, Michigan

This former underground gypsum mine in Grand Rapids, Michigan was converted into a produce storage warehouse in 1957. Its caverns are accessed by elevators operating inside two vertical shafts. Additional freezers and warehouses have been built on the surface. Around 750,000 square feet is said to be available for use still, underground. In 2001, the Underground Secure Data Center Operations company (USDCO) opened a data center in the mine, which has since changed hands.