Taking its cue from some of the more extreme obstacle-course races for adults, the Keen Kids Adventure Games at Vail sends pairs of kids, ages six to fourteen, careening across mountain-bike trails, ziplining across a creek before tubing down it, and getting all manner of dirty in challenges that include a slackline over a mud pit, a giant Tarzan-style swing and an enormous slip-and-slide down a ski slope. Teams typically finished the 2013 course with times in the 45-minute-to-two-hour range, gleefully exhausted and ready to throw their sneakers in the trash. The 2014 race will be held August 6 through 10.