If you like spectacular views within a short ferry ride from San Francisco, Oakland or Tiburon, I highly recommend visiting Angel Island. I rented a bike for the day (www.blazingsaddles.com--negotiate the price--as they are more competitive than rentals on the island, which operate seasonally) and was able to leisurely circle the island, hike to the top of Mt Livermore (nearly 360 degree view) and stop at various historical and scenic sites. Another relaxing way to see the island is to take the tram tour.
I never knew that Angel Island served as a US Immigration and Station between 1910-40, a Quarantine station 1891-1946, a US Army Camp beginning with the Civil War and a Nike Missile site during the Cold War in the 1950's. Most of the island became a CA State Park in 1963. There are exhibits and videos that do an excellent job recreating what it was like for the largely Chinese population that were detained there before being granted entry. I suggest about 1 hour is needed to explore the Immigration area ($7/person for self-guided tour), which is about a 20 min bike ride or 30 min hike from where the ferry lands.
To make the most of your time here, I suggest catching the first ferry in the morning and the last one back (www.parks.ca.gov.angelisland). Definitely bring water and sun screen with you, as well as, food or snacks. There is a snack bar on the island but believe it is operated seasonally. There are also camping sites that can be reserved (www.parks.ca.gov).
If you own or manage Angel Island State Park, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.