Some advice everyone will give you, but nobody seems to follow. When you go see the wall, see it at Simatai, not Badaling. Badaling is about thirty minutes from Beijing, and the destination of every tour bus. As a result it's completely packed, even in a China context. I've included a Badaling photo from the internet as a point of comparison, but I've seen it much worse, where you literally don't walk on the wall, you just get carried with the human tide and hope you don't get trampled to death. To make matters worse, this part of the wall is almost entirely a reconstruction. So you must go to Simatai, where the setting is more majestic, the wall is entirely authentic, and there are 99 percent fewer tourists. It's about a two hour drive, but it's an infinitely better experience. I assume you can tell which photo is which, so I won't elaborate.