on the last friday of every month, hundreds of cyclists converge upon the streets of chicago, en masse, to show how beautiful life can be upon two wheels. they call it critical mass.

in july's mass, 700+ cyclists rode mainly through the loop, and then, in an echo of may's event, on lake shore drive from jackson to fullerton -- a 3.5-mile stretch. it was exhilarating.

we finished up the ride at oz park, which is guarded by a very reflective sculpture of the tin man.