My friend sent me this link:
The FELIS 50
It's a reasonable challenge to do. Sure, this guy is doing it March 1st here in New Jersey, but it's one you can try on your own. Find a field marked out to 50 yards, load a bag to 50 pounds, and walk it back and forth 50 times. That's 2500 yards or a bit under 1.5 miles.
If I'm not working that day I want to do it, just to see how it goes. It's not a hard challenge to do anywhere - whether you're in New Jersey or New Guinea, California or some Siberian outpost.