Fort Knox Bullion Depository

The United States Bullion Depository at Fort Knox, Kentucky, is a fortified vault that holds a large share of the nation's gold reserves. Built in 1936 of granite, concrete, and steel next to the Fort Knox Army post, it is protected by a blast-proof vault door, layered security, and the surrounding military base. No visitors are permitted inside — the phrase "locked up tighter than Fort Knox" became shorthand for impregnable security.

• Kentucky
  The Bluegrass State, between the Appalachians and the Mississippi related