If you click through travel Web sites and flip through adventure brochures, well-known tourist destinations seem to be about the same things: sightseeing, shopping, dining and taking photos. But if you're looking for more of a challenge, these 10 landmarks will get your blood pumping. Even if you're not overweight, and even if you eat a fairly nutritious diet and hit the gym a few times a week, you'll need to train specifically to achieve the physical and mental fitness it will take to reach the destinations on the next pages.