Places to see: Check out the web sites for all these for open days and times, and admission fees.
Muir Woods- Coast Redwoods, hiking, pretty good view from one of the longer (uphill) hikes, Beaches nearby.
Fitzgerald Marine Reserve- Go at low tide.
Mount Diablo- Great views on a clear day.
Napa and surrounding wine country, and California Carnivores. Giant greenhouse set up for growing and sale of carnivorous plants.
Bancroft Garden- Ruth Bancroft traveled the world and brought back all sorts of odd plants, about half or more are succulents. 2 greenhouses and several acres. (Admission fee is a bit much unless you are really into this sort of thing)
UC Berkeley Botanical Garden- plants from all over the world, including carnivorous plants, tropicals in greenhouses and many oddities.
Tilden Park Botanical Garden, specializing in CA natives.
Lawrence Hall of Science
San Francisco:
Strybing Arboretum
Japanese Tea Garden
California Academy of Science, including Steinhart Aquarium (A bit pricy, but well worth it)
Pier 39 and the rest of Fisherman's Wharf
Aqua Forest, Amano's ADA outlet
China Town, an area of SF with a very large Chinese population, great food, lots of stores.