You have to move fast for this one: Last year, the 1,500 slots for the 7-Mile Bridge Run, across the longest of the Florida Keys' 43 bridges, were snapped up in a mere 10 minutes. (If you're skunked, you can bid for one of 10 additional slots on eBay.) Not up for a quarter-plus marathon? The Cow Key Channel Bridge Run, across one of the Keys' shortest bridges, claims to be the world's only Zero K run. A crazy costume is de rigueur, one of the heats features pets with humans, and there's a bar at the finish line.