There is a zipline about 200 metres west of the back gate at the top White Pagoda Hill Park (白塔山). There are photos below, and a promo video on Tudou (which is pretty good, if you can ignore the 'busy' webpage). You can also do a zipline at Xinglong Shan (no photos).
Nicola came to visit, and these are some of the things we did...
Took photos by the "Journey to the West" sculptures
Chinese: 兴隆山 (Xīnglóng Shān), 栖云山 (Qīyún Shān)