I didn’t think any visit to San Francisco would be complete without a trip to Alcatraz. I think the prison is famous worldwide. To get there you need to take a ferry. The website suggested pre-booking, and I did, but it didn’t seem necessary at Pier 41. Perhaps in the high season it is a good idea to pre-book.
One of the interesting parts of Alcatraz that I did not know is that after the military stopped using it as a prison it became a base for an aboriginal movement. This water tower was apparently rusted through so it was sanded down and repainted, but they found the decendents of the original “artists” to repainted the messages.