Sutro Project / Angel Island
Alcatraz's bigger and less-developed sibling, Angel Island provides unbelievable views on 14 miles of trails - truly a hidden gem! Hiking and biking are recommended. Tram and a Segway tours are also available.
Ferry Service runs from Pier 41 and the Downtown Ferry Building (or Sausalito and Tiburon if you're in Marin County already).
Wikipedia: http://en.wikipedia.org/wiki/Angel_Island_(California)
