The Explorers Series: Casey Brown

Mountain biker Casey Brown is already one of the fastest mountain bike racers in the world. But because ripping down mountains at 50 miles per hour isn't quite thrilling enough for her, she's now into freeriding, an extreme discipline that essentially involves riding down the sides of massive cliffs, sending huge air along the way. It's the sport's version of big-wave surfing, and typically only attracts male riders with huge risk tolerances. Until Brown came along.