Sutro Project / Crissy Field
After serving as a landing site of early explorers, hosting the Panama-Pacific exposition, and serving as a airfield for the army, Crissy field now offers visitors a great way to get away from urban San Francisco and enjoy the bay's natural beauty. It's about a 4 mile (round trip) walk from the Palace of Fine Arts to the Golden Gate Bridge. Depending on the weather, visitors are joined by seals, seagulls, joggers (and the Marina District has some very attractive ones!), dogs, picnickers, sailors and surfers (wave and kite) enjoying the bountiful locale.
It can get cold and windy. Stop by the locally loved Sports Basement for warmer clothing, and the Warming Hut for a cup of coffee.
Wikipedia: http://en.wikipedia.org/wiki/Crissy_Field
