Come summertime, the world-class ski slopes of Park City (home of the Sundance Film Festival) make for possibly the best mountain biking in the world: The region is the only one to hold the International Mountain Bicycling Association's highest designation. Offering 400-plus miles of wild trails, the area is enticing for bikers of every skill level. Beginners can meander across bluffs and through Gambel oak on the Round Valley Loop Trail. The aerobically fit should tackle Wasatch Crest, which climbs to 10,000 feet and delivers outstanding views of both sides of the Wasatch Range.