Goto the Great Wall at Simatai, about 2.5 hours northeast of Beijing. You must walk up a fairly steep section of the Wall along a mountain ridge. The cache is hidden near a trail that branches off from the Wall and onto the mountainside. The views are spectacular and this is one of the less touristy sections of the Great Wall.
The cache is a small tupperware box wrapped in a black plastic bag. It contains a few items of memorabilia from the U.S., along with a disposable camera and a log book.
The hike is not very difficult technically, but walking up all those steps on the Wall is physically challenging.
I could not say enough about the local scenery -- it is a sparsely populated, mountainous area that is incredibly beautiful.
Enjoy!