There are many reasons to visit the (free!) Cable Car museum (Original equipment! Original building! Walkable from the California line!)

but, my favorite is the Victorian stereoscope machines.

Drop a quarter into a machine and enjoy a flip through Victorian San Francisco highlighting before and after stereoscope photos the 1906 earthquake and fires.

Tip: As you exit the museum and cross the street, look for these access panels in the street where you can listen to the constant hum of the continuously running cables.