For folks in the Bay Area, a challenge: Do a loop around the bay by non-commuter bus only. That means you can use skip-stop routes like Muni's 9R, but you cannot use routes like AC Transit's OX line. You also cannot use the Dumbarton Express, since it cuts off the South Bay.

It's an interesting experience, and it (or some portion of it) is one that many folks do every workday.