The Presidio (San Francisco, CA)

At the foot of the Golden Gate Bridge is the 1,491-acre urban park, the Presidio. What started as a Spanish military fort in 1776 later became a U.S. Army post in 1846 before turning into a national park in 1994. The 24 miles of hiking trails and 25 miles of biking trails are all open to runners. Zip through eucalyptus forests or pound the pavement by Crissy Field with sprawling Bay views.