Zhang Xiaodong, former assistant manager of the 816 underground nuclear military plant, introduces the history of the plant in Fuling, southwest China's Chongqing Municipality, Sept. 25, 2016. The 816 underground nuclear military plant, once a highly confidential military base, opened to public on Monday after renovation. The base was built in 1960s and first opened to tour groups in 2010. (Photo/Xinhua)
