Affectionately known as 'The Rock, Alcatraz Island in the San Francisco Bay is a former prison with a long and amazingly well-documented history. 

In the 1800's Alcatraz was a military prison, and then in 1933 was converted to a federal penitentiary until it was shut down in 1963. For six years the space lay mostly dormant, until a group of Aboriginal Peoples from San Francisco occupied it for 19 months as a part of the Native activism movement that was sweeping the nation in the late 60s - early 70s. In 1972 the island became a recreational area, and it became a National History Landmark in 1986, so it is now fully protected.

The island is 1/5 miles from the shores of downtown SF, which doesn't seem like too far of a swim for an escaped prisoner, but a visit will change your mind; the treacherous riptide currents and bone-chilling water make the swim nearly impossible. The audio tour (highly recommended) takes you outside to a part of the yard where SF is visible and tells you to imagine that you are a prisoner looking at the city, knowing that escape is impossible. The isolation and despair are palpable.

The hybrid propulsion ferry at Pier 33 near Fisherman's Wharf takes you to Alcatraz, which is another bonus, since hybrid boats are pretty new technology, and pretty awesome.

In addition to the prison, 22-acre Alcatraz Island is also home to the oldest operating lighthouse on the west coast, many old military ruins, and plenty of nature to explore. Wandering the trails, you'll find rock pools, a large colony of seabirds. I spent the whole day there, and barely scratched the surface. Don't miss it.