You don't have to travel to another continent to find a challenging trek. The Bright Angel Trail is one of the few trails that visitors to Grand Canyon National Park can use to journey from the canyon rim down to the Colorado River. This trek is not for the faint of heart. The trail is 9.5 miles long and descends more than 4,500 feet (that's just short of a mile in elevation change). Most visitors attempt a short section of the trail, turning around at one of the early “rest stations” that are placed at intervals along the path. Why go all the way? Because the views are tremendous and experience of walking down one of America's great natural landmarks is truly unique. The steepness and altitude make this a challenging hike, but the biggest danger is the temperature. This is not a morning walk, but a daylong journey (actually the National Park Service warns against making the top-to-bottom-to-top trek in one day) in temperatures that routinely top 110 degrees. Much of the trail is completely exposed to the sun, so people who are not prepared to handle the heat will find themselves in danger rather quickly.