The audio tour is very well done and is free along with the price of admission (includes the ferry ride).
Each person gets their own handheld device and the recorded voice tells you where to turn, where to stop, etc.
If you are planning a trip to SF, allot about 4 hours or so. When you are at the top part of the jail, you can walk out to some absolutely breathtaking views of the city, and you can also take photos from the boat with the skyline in the background.