One of San Francisco's main attractions, this infamous island-prison tour lets you experience how the inmates here lived. You can visit cells, while a tour guide explains the history and the stories behind the prison itself, and some of it most (in)famous residents. Special attention is given to the legendary single successful escape from the island prison, and, naturally, to Al Capone, its most famous inmate. Another obvious benefit are the wonderful views of the San Fransisco skyline and of the Golden Gate bridge.
All in all, the tour is informative and this is certainly a must-see in San Francisco. The drawbacks are that you are on the boat's schedule as far as the return trip is concerned.