Chinese tourists visit the China 816 Nuclear Military Plant in Chongqing

Chinese tourists visit the decommissioned, once top secret, China 816 Nuclear Military Plant buried into a mountain in Fuling District, a few hours outside of Chongqing, one of four direct-controlled municipalities in China, on November 5, 2016. The abandoned military nuclear facility, hailed as the world's largest man-made cave system able to withstand atomic and hydrogen bombs, has recently opened to tourists. It was designed to manufacture nuclear plutonium in the 1960s but was stopped from doing so in 1984. Photo by Stephen Shaver/UPI