Bikeability is a key component of livable cities, and the best cities have the best group bike rides. Themed rides are like themed parties; they’re a great way to attract riders and make a long bike ride festive and memorable. I’ve seen tweed rides, seersucker rides, full-moon rides and more, but it’s hard to top a naked bike ride. The one in Philadelphia, only five years old, is apparently the 2nd-largest in the nation. I took a folding bike on Amtrak to join the ride and tour Philly while surrounded by naked bicyclists.