There's an event here in San Jose called the San Jose Bike Party, that occurs every month on the 3rd Friday. The rides start at 7pm and depending on your riding speed, can end anywhere from 11-Midnight. Most rides average around 30 miles, though one might be longer if you have further to ride to get to the starting point. The routes change with every ride and explore the entire South Bay area, passing through surprised town after town until they end in some plaza or park in an unsuspecting downtown. I say "surprised" and "unsuspecting" because the amount of riders can be anywhere from 1000 to 4000 people. The police aren't generally notified of the swarm's planned route, though I know that for the ride through Campbell's downtown the police were contacted to help direct traffic (the downtown area is very small). There's nothing like seeing 3000 riders come blazing by in skulls and pumpkins (the rides are themed).
So far I've only participated in two rides, but each one was a blast. The first ride was just before Halloween and had a Day of the Dead theme. The ride last weekend had a theme of the Running of the Bulls. Not as many people were dressed up for the recent ride, but it was still a lot of fun. Total distance was 28.4 miles. I was very excited to start the ride, almost couldn't get the camera to focus on me. Of course, at the end of the ride I fell asleep on my couch while I had company over, but who's thinking about that?