Engadin Ski Marathon, Sils, Switzerland
More than 10,500 skiers participate in the 26.2-mile race between Maloja and S-Chanf near the Swiss mountain resort of St. Moritz.
Marathon des Sables, Ouarzazate, Morocco
The Marathon of the Sands takes place over six grueling days, and stretches 156 miles, the equivalent to six regular marathons. The longest single stage is 52 miles long.
Ironman Triathlon World Championship, Kailua-Kona, Hawaii
This classic test of stamina combines three endurance events -- a 2.4-mile ocean swim, a 112-mile bike ride across the Hawaiian lava desert, and a 26.2-mile marathon along the coast of the Big Island. The current course record is 8 hours 4 minutes and 8 seconds.