You can rent mountain bikes with helmet and bike lock from Dōngfāng Wēinísī Jiǔdiàn (东方威尼斯酒店; literally 'Venice of the East Hotel'), a small hotel just outside West Gate. It takes about one hour to cycle to Southern Great Wall; head west along Hongqiao Xilu, turn left at the roundabout, onto Tuqiao Lu (土桥路), and keep going. Huángsī Bridge Old Town is 10km further, on the same road.