A bunch of people running in the streets in speedos, or how a small holiday stunt turned into a national phenomenon.

The Boston tradition known as the Santa Speedo Run began on a Saturday, in December of 2000, when 5 friends decided to do something completely crazy to spice up their weekly routine. The best they could come up with was running through Boston wearing nothing but speedos, Santa hats and fake beards. They tried to get another 20 runners involved, but one week later, at race time, it was still just the five of them.

But they kept their courage and went through with what the plan. People shopping on Newburry Street started screaming and cheering while the five naked Santas ran by. And that, in short, is how the Santa Speedo Run was born.

It has come a long way since then, turning into an annual charity event that raises money for various charities, and inspiring similar displays in other American cities. Anyone can enter the Santa Speedo Run as long as they raise the minimum $250 for charity and aren’t afraid to strip down to their speedos at race time.

Photos via Boston.com