The Great Wall of China. While it's photographed so often, no photograph that I have so far seen truly captures the absolute marvel of its size. Not only its size, but the fact that much of it was built on the tops of these sheer peaks truly astounded me.
Having a chance to climb up parts of the wall was magnificent--I tried to imagine how well-trained the soldiers must have been, to climb up the irregularly-placed, ladder-like steps. (In fact, in the touristy areas, the steps have fences placed at different places in the middle of the stairway, making a kind of maze; I was pondering why the tour companies might have done this, and then it struck me: the fences were meant to limit your fall: if you were unfortunate enough to slip at some point, you might get slightly injured--but you wouldn't suffer more than a few scrapes and bruises. Were the fences not there, well...)
The view from the wall is absolutely astounding--while seeing it stretch its way over hill and dale out past the horizon, a thought suddenly struck me with sheer awe: we (people) built this?!