It is called the LATE Ride. It is put on thru the Friends of the Park and it is a total blast. I have been doing it for about 10 years now. The ride is 25 miles (sorry I am a dumb American and do not know the metric equivalent). It starts downtown and loops around going west, north, east and south. You end up where you began. It starts at around midnight, but really you don't get going until b/w 12:30 and 1 a.m. You see the City at a time that you generally don't see it (because you are either asleep or too drunk to remember). I love this ride! It is the best one that is out there. And for those in the know, no I do not like Bike the Drive, generally it is still way too cold to ride 15 miles north fighting the wind and 15 miles south (also fighting the wind for some strange reason).
Friends of the Park also do the Naked Ride. Yup, you saw that right. And let me assure you, most of the people who do the Naked Ride should really NOT be naked. And to set the record straight, no I do not do the Naked Ride. When your family jewels are in your chest, you cannot go w/o your over-the-shoulder-boulder-holder.
If anyone else is doing it ...HAVE FUN!