Grand to Grand Ultra, USA
Credit: Mark Hannaford / Getty Images

Who: 120 runners

When: September 21, 2014 and 2015

Why it's unique: Run, don't walk (or drive) from the North Rim of the Grand Canyon, on a mostly sandy path, past remote hoodoos and buttes, though a tributary of the Virgin River, and at least one isolated slot canyon until finally you reach the top of the Pink Cliffs of the Grand Staircase. It's a six-stage, mostly self-sufficient seven day course – 170-miles in total, where you're camping each night, and required to pack and carry all the food and clothing you'll need. Even with a night's rest between stages, 15 percent of entrants drop out before the finish line. [g2gultra.com]