As a recent transplant to the West Coast I am constantly making new discoveries, most of them pleasant.
A museum that I have never heard of is the Legion Of Honor http://www.famsf.org/legion/.
A magnificent building itself houses these great works of art. A fit setting for this collection of major masters. The permanent artists include well known sculptors including Rodin. Most everyone knows the Thinker. But what about a silver Hercules battling a six headed dragon? They are all there.
There is always a temporary exhibition, currently we see Cartier Jewelers. Prior to that Egyptian Art and Mummies filled the massive granite hall.\
It is located on cliffs overlooking the Bay with a great view of Bridge Golden Gate Bridge.
Twenty bucks will get you in and you can always become a member. It might be worth it depending on how often you go.
There are also nice hiking trails all around, eventually taking one to Lands End.