7. Arrowhead 135-mile Winter Ultramarathon: Of the 59 racers who started this "human-powered" challenge February 2, less than half were able to finish. It's no wonder: The 135-mile bike, run, or ski challenge takes place in some of the Lower 48's most extreme winter conditions, along the Canadian border in Minnesota's remote Arrowhead Region. Skating across the frozen finish line on February 4 were 15 cyclists, eight runners, and one skier. Learn more on the race blog, here: www.arrowheadultra.com/blogger/blogger.html.
6. What makes the Manhattan Island Marathon Swim the toughest open-water race in the country? Aside from the boat traffic, frigid choppy water, and long distance—racers complete an entire 28.5-mile circumnavigation of the Big Apple—swimmers have to contend with "random jetsam and flotsam in the waterways," according to the official race site (www.nycswim.org). We don't even know what that means, but… it sounds pretty bad.