City Challenge Obstacle Race LLC, New York

Imagine a major US city overrun with people leaping over police cars and taxis, sprinting while hauling water jugs and sandbags, and scaling ropes that dangle alongside the skyline. No, they're not actors filming an action scene for a TV show—they're participants in the City Challenge Race.

During the event, the city sprouts more than 20 obstacles that athletes tackle along the 3.5-mile course. Women and men scale walls, carry heavy objects, and lug the ceremonial key to the city through the streets toward the finish line. Once there, they can high-five each other and themselves over a challenge completed as well as funds raised for charity.