Presidio of San FranciscoPresidio of San Francisco

Used as a fortified military base from 1776 to 1995 by Spain, Mexico, and the United States. It is now part of the Golden Gate National Recreation Area and serves a mix of commercial and public uses. It is required to be financially self-supporting by 2013. Photo: Robert Campbell, CC BY-SA 3.0, via Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Aerial_view_-_Presidio-whole.jpg)