transitmaps:

Wonderfully immersive visual history of transit in San Francisco. As the blurb on the site says:

The history of San Francisco’s transit system can be traced back as far as 1873, when the first cable car began service. Tales of technological advances, natural disasters, political struggles, and triumphant celebrations color its 140-year history and shape it into a system today that’s uniquely diverse and uniquely San Francisco.

Definitely worth losing a few hours to!