One of the city's best free offerings, this museum is an absolute must for kids. You can even ride a cable car here—all three lines stop between Russian Hill and Nob Hill. The facility, which is inside the city's last cable-car barn, takes the top off the system to let you see how it all works. Eternally humming and squealing, the massive powerhouse cable wheels steal the show. You can also climb aboard a vintage car and take the grip, let the kids ring a cable-car bell (briefly), and check out vintage gear dating from 1873.
The gift shop sells cable-car paraphernalia, including an authentic gripman's bell for $600—it'll sound like Powell Street in your house every day. For significantly less, you can pick up a key chain made from a piece of worn-out cable.