The San Francisco Exploratorium
I have heard of the San Francisco Exploratorium for as long as I have lived in the Bay Area. Ironically, I only made my very first visit to this very popular interactive Science museum last week.
For a limited time, California teachers get in for free. Otherwise, general admission is $29 or $22 for SF Bay Area residents.
I am not a Science buff but I did enjoy myself here. On the other hand, Marc loved it a lot and he could actually have stayed a lot longer than the four hours we spent here.
It is along the Embarcadero waterfront and is walking distance from the Ferry Terminal. Definitely easy to get to when visiting the city and you want to visit a museum different from the usual viewing of works of art and classic masterpieces.