Alcatraz, a rocky island about a mile off San Francisco Bay, is famous for being a federal prison from 1933-63 and housing notorious criminals like Al Capone and 'Machine-Gun' Kelly. Also known for its countless escape attempts, the most famous being depicted in the movie "Escape From Alcatraz" starring Clint Eastwood.
There are tours to Alcatraz from Pier 33, usually having to get tickets in advance online. Or, a better alternative might be the Blue & Gold Fleet's 'Escape From The Rock' cruise easily located at Fisherman's Wharf, taking you under the Golden Gate Bridge and around Alcatraz with a Wi-Fi audio tour. No waiting, with first-come-first-served at the gate.