Alcatraz Island offers a close-up look at the site of the first lighthouse and US built fort on the West Coast, the infamous federal penitentiary long off-limits to the public, and the 18 month occupation by Indians of All Tribes which saved the tribes. Rich in history, there is also a natural side to the Rock—gardens, tide pools, bird colonies, and bay views beyond compare.
Visiting Alcatraz is partially a self guided experience which you can do at your own pace. Park Service staff offer numerous free programs throughout the day on a variety of topics: escapes, military history, American Indian occupation, natural history, etc.
Once on the island you can stay as long or as short as you wish - there is a ferry departing about every half hour and you can return to San Francisco on any ferry. We generally recommend at least 2 to 3 hours to fully visit the island.
There are numerous videos and exhibits on the island, as well as the cellhouse audio tour which is included in the price of the ferry ticket.