Washington Navy Yard
Established in 1799, this is one of the oldest operating Naval facilities in the U.S. With an amazing 2 million square feet of space and over 16,000 employees, the Navy Yard is bigger than a lot of cities in area and in population. With a museum, food court, and shops, it's got all the amenities of a small city too. The museum is interactive where you can sit in a submarine control room and climb on top of the gun turrets - especially interesting for kids. Expect that if you visit, your bags will be inspected by MP.