Madison Naked Bike Ride: June 18th
They do not promote it much, if at all. The actual meeting place is not announced, instead the day of the ride they announce a checkpoint where they take riders in groups to the start point. There is a strict deadline to be at the checkpoint. Their policy is if you are late, try again next year. I headed out early, had a flat tire on my bike, and just barely made it on time. Fortunately, I carry a spare tube and small air pump. They do not, as far as I know publish a map of the route. Can you imagine how pissed off I would have been if I missed the ride after driving 23 hours to get there? Chicago does a similar procedure, but posts a route map the day of the ride, so if you are a little late you could catch up with the group.
Because there is little or no promotion the spectator count, with the exception of the Capitol Circle area, where there was a farmers market type thing going on was quite low. I don't think we had more than 100 spectators the first couple miles.
There is a Meetup discussion group with updates and pics and video of this years ride. https://groups.io/g/MadisonWNBR