Obstacle Racing has become a pretty big thing in the last few years... and if you haven't tried one, you should. They are ridiculous fun. There are a variety of different types ranging from simple, fun 5ks that families can run all the way up to the World's Toughest Mudder -- which can be as long as 90 miles of grueling torture. What obstacle do you dread the most? That you see coming and grit your teeth? Vote, and Add any I missed!