Today's photo is in fact a video, which I found on YouTube. I live very near the Millenium Bridge, and these cyclists are going across it at the start of the vid. Then they turn right and proceed into town down Terry Avenue, the same route I go on by bike just about every day. But the difference between me and most of these cyclists, is that I wear clothes when I go out on my bike ;-)
P.S. Check the screeches of horror at around 3.20 - 3.30 in the video. They happen as the cyclists are going past the gates to Rowntree Park, where there is a skate park / youth hang out. "AAAAAAARGH! LOOK AT THAT!"
Addendum: I've just found this, incase anyone is interested in knowing more - or indeed participating next year: World Naked Bike Ride UK.