During my many business trips to China, I was fortunate to get to the Great Wall north of Beijing on three occasions. Taking a cable car up to the mountain ridge on which that part of the wall is sited, walking the ramparts, and watching the wall sinuously wander over the hills and valleys in both direction as far as you can see is an overwhelming experience. The section of the wall, I've walked is at Mutianyu (photo below).
It's also an experience that inspires the question, "What the heck were they thinking?". Why build a wall on top of a mountain? A mountain is a pretty effective wall in itself. Enemy armies and raiders don't climb razor edge mountain ridges in order to attack. They move through valleys, fields and low open hills. One can be impressed by the structure, in awe (and horrified) at the difficulty, material and human cost of its construction, and simultaneously appalled that it was built just to demonstrate it could be done. Of course, we should remember the Wall also crosses many of miles of desert and lowlands.
I recently learned of an Englishman, William Lindesay, who's spent the last 30 years exploring the entire length of the Wall, from its eastern end on the Manchurian coast to the edges of the Gobi Desert (the total length is 3,000 to 4,000 miles). Most recently, he was given permission to fly a drone above the wall as he and his family trekked its length, which has provided us with some amazing footage. You can find the BBC story with an embedded video here. His website with stunning photos can be found here. And below is a video containing spectacular footage from Lindesay's drone.