Presidio of San Francisco, California

1,480 acres of scenic urban land at the base of the Golden Gate Bridge in San Francisco, contained within the larger 75,500-acre Golden Gate National Recreation Area (GGNRA), the world's largest national park in an urban area. The Sixth Army still has a presence of a few hundred people here; they pay rent to the National Park Service, which inherited the base when it was officially closed in 1995. In 1996, in what was then an unusual public-private partnership, the U.S. Congress created the Presidio Trust, a new federal agency charged with managing the site. Their mandate, however, came with the added obligation to either make the park financially self sufficient by 2013, or run the risk of its being auctioned off. In 2013, the goal of financial self-sufficiency was achieved, despite The Presidio continuing to be the most expensive park to maintain in the National Park System, due to its extensive collection of buildings (over 800), in addition to a golf course and a national cemetery.