It’s a very Oregonian thing, you see. It’s the World Naked Bike Ride, in which 5,000+ residents show up downtown, take off all their clothes, and pedal about. They also visit museums. I’ve been to a surprising number of Oregon events where people just shuck off everything, completely unselfconsciously. Damned hippies. Gotta love ’em.
There are photos at the link, but mostly tasteful — at most you’ll be flashed with a few bare butts.