Calling all endurance athletes ready for a real test of mental toughness: Dominion Endurance's Founders Challenge is a 12-hour grind where you'll complete one mile every hour on the hour while carrying minimum weight (35 lbs for men, 25 lbs for women), with no excuses or shortcuts allowed—miss a single hour and you're done. On that final 12th mile, you'll add at least 10 pounds more to your load and carry it however you see fit, whether in your hands, on your shoulders, or dragged behind you. This virtual, self-directed event lets you pick your own route and terrain anywhere, but there's one rule that matters: make it brutally hard.