From the FaceBook event page:

Meet at 6, ride at 6:30.

Rain, fascism, or shine.

Our usual meeting spot in Monroe Park has been fenced off for renovations for the next year or more… For now we will meet at the same intersection, just across the street on the sidewalk in front of Altria Theater, to avoid too much confusion. A different meeting place may be chosen in future months, so keep an eye on the location!

What is this event?!

http://en.wikipedia.org/wiki/Critical_Mass_%28cycling%29

Last Friday evening of every month! Come out on your bikes and ride en masse through the city, for any number of reasons: just for fun, to celebrate bicycles as an alternative to cars, to spread awareness that bicycles share the road, or as a form of political protest. Wear costumes, bring music, noisemakers, flags, ribbons, etc. Ride a skateboard, roller blades, unicycle or some other human-powered bike alternative. Make it a parade!

Many interesting routes (and stops) are planned in advance, but some are unplanned and can simply be determined spontaneously by whoever is riding in the front. Ride SLOWLY so we can all stay together, enjoy the ride, talk along the way, and encourage people to join us.