Tour Divide mountain bike race from Banff to Antelope Wells, NM. over 2700 miles, and over 200,000 feet of climbing on a mostly unmarked trail. Totally unsupported, no GPS allowed. Winners take over 18 days.
But, such an event does not really attract the World's best athletes. There is an exclusive club of idiots who do these solo ultra-endurance events. While they are strong athletes and in tremendous condition, I do wonder what would happen if Tour level cyclists started riding in these things.