洮河
Surrounded by a maze of hills and valleys, Niangziguan Pass was famed as "the Ninth Pass on the Great wall". The extant pass was built in 1542 during the Ming Dynasty. The pass is flanked by hills more than 1,000 metres high. A river, the Tao River, twists its way through the valleys below. In ancient times this provided a narrow passage for men and horses.