To say this is one of the most difficult treks inside a man-made structure is like saying there's some water in the Atlantic. But exploring Egypt's lesser known Bent Pyramid, is an exercise is stamina, and claustrophobia. It's 85 meters down in a narrow shaft that requires you to bend at a 90 degree angle. Then it's an 85 meter climb and crawl though even narrower shafts to its cathedral-like ceiling. It's not for the weak (if you have a heart condition, I would suggest you stay out of the interior). For me it was quite the adventure. And oh, so worth it (look at all that sweat!).