From the Facebook event page:
Historically, October’s critical mass was the largest ride of the year in Baltimore, let’s bring that tradition to the Bike Party! I know we can break 1000 riders (yikes!!!).
This month’s theme is pretty obvious, we want to see everyone in costume! We want you in costume, your bike in costume, your cat in a basket dressed like ET.
Find out more and RSVP on Facebook.