Critical Mass bicycle ride
Michael Bluejay has this one covered: criticalmass.info, though I'm linking to another site below.
I've been on CM rides in Seattle, DC, NYC, Austin, and possibly elsewhere. Different cities at different times had different flavored rides. Some were crazy and militant (laying down in intersections), others were peaceable, law-abiding (stopping at all lights), and themed (e.g., Monica Lewinsky affair ride in DC). I never was a CM devotee, but went at least once in each new city I lived in, in general. Now, after riding across most of the US and some of Mexico, I've just about had it with ever bicycling on the same road as cars... I'd rather never be around cars. And I get impatient with the bicycle--it is after all another machine, and has many of the problems of cars, but in miniature. These days I walk or run. One place I loved to ride was northern Virginia, on a circular route that took me on carfree bike paths and the wonderfully peaceful & beautiful carfree C&O canal, and over the Potomac near the inspiring Great Falls, and on very car-lite suburban roads.