The Hounslow Classic ultramarathon, held in the Blue Mountains of Australia, is widely regarded as one of the best ultramarathons in the world. The race, which is 68k with a total elevation gain of 4800m and a 17 hour cutoff, offers runners a truly unique and challenging experience. The Blue Mountains are known for their stunning natural beauty and diverse terrain, with waterfalls, overhangs, dirt roads, and dense forests all making an appearance on the course. In addition, the Blue Mountains are a more lush and varied version of the Grand Canyon in the United States, making them a truly special location for an ultramarathon. The Hounslow Classic also attracts a high caliber of runners, with many participants having summited Everest or completed other impressive feats. All of these factors combine to make the Hounslow Classic ultramarathon one of the best in the world.