Escaping from Alcatraz may be a little too intense for some folks, but if you're keen swimmer and you're heading to San Francisco you should check out Water World Swim. They organise monthly group crossings of around 20-49 people in a non-competitive environment - all you have to do is just keep swimming.
For people who want to stay on dry land, why not build a day around visiting the former federal prison? Be advised: Tours often fill up early so you’ll want to book your visit several weeks in advance. Consider a side trip to Angel Island, the largest natural island in San Francisco Bay.
If, after watching this video you think that Jonny is a total legend, be sure to find out more about his love of California in his California Questionnaire and then listen to him talk about his Lake Tahoe favorites via the California Now Podcast.