Bright Angel Trail, Grand Canyon, Arizona
Credit: Demetrio Carrasco / Getty Images

That the Grand Canyon might present visitors with some challenges should surprise precisely no one. But until you've actually made the visit to and then down in, you may not appreciate how extreme the environment can get. And the most notorious hike is the 9.5 mile Bright Angel Trail that runs between the North and South rims. On paper it's not a bad run, until you consider that temperatures regularly pop over 110 and that the approach is a long steady, draining, uphill slog. Despite plain warnings everywhere, some 250-odd people a year need to be rescued from the trail for heat-related ailments – so many that the National Park Service assigns a specific crew just to keep tabs on Bright Angel visitors.
[nps.gov]