The Academy of Sciences is pretty cool, and it makes a visit to Golden Gate Park more than worthwhile. Since the new building opened, the Steinhart Aquarium & Morrison Planetarium are better than ever.
http://www.calacademy.org/
Also in the park, very close by, the Japanese Tea Gardens and the De Young Museum.
Fisherman's Wharf and North Beach are pleasant except for the lack of parking. To me those neighborhoods are better for walking (with hills, in N. Beach).