Every third Sunday in May the runners--and party animals--of San Francisco lace up their shoes for Bay to Breakers, a 12K race from the Embarcadero to Ocean Beach. There are plenty of serious racers in this event, but it's also a chance for people to dress up in costume and indulge their silly side, like a group dressed as salmon who run "upstream" against the crowd. Many people make elaborate costumes and walk the course, stopping for beer along the way.

baytobreakers.com