Alaska Ultra Sport's Iditarod Trail Invitational is the world's longest human powered winter ultra-marathon.
Crossing 350 to 1100 miles of frozen Alaskan wilderness, it is a brutal contest that few enter and only about half finish.
This year 50 riders and skiers have signed up to take their places at the start line in March 2009.
See for yourself in this video from the New York Times.
Insanity on wheels. You gotta love it!