Pentagon, Virginia

Headquarters for the United States Department of Defense, and located across the Potomac from Washington DC. The 5-story building, with 17.5 miles of corridors and 6.5 million square feet of office space, is regarded as the world's largest low-rise office building. From 1992 to 2011, the Pentagon underwent a full-scale renovation at a cost of $4.3 billion, in order to bring it up to current health, safety, security, and fire codes.