Inside China's top-secret nuclear town known only as '816': How Beijing tried to build weapons of mass destruction in the world's largest man-made cave during the Cold War

In the mid-1960s, China began to build a top-secret nuclear plant in case of a surprise attack from the Soviet Union. It was such a secret project that its location was scrubbed from every map and even the facility's builders didn't know its true purpose. This week, Chinese state media revealed new details of the mysterious plant, which has since become a neon-lit tourist attraction. Scroll through to see these amazing photographs...

Construction of the mysterious 816 Nuclear Military Plant, near Chongqing, began in 1966 under the direction of Chairman Mao, the country's founding father.

Beijing kick-started the project at the height of the Cold War to boost its defense against the Soviet Union. It remained a top-level secret in China for 17 years and was largely constructed by the 54th Division of the People's Liberation Army.

Soldiers from across the country were sent to Bailang Town to chisel a network of caverns and tunnels out of mountains. The site, with an unusual underground reactor, was designed to tolerate thousands of tons of TNT explosives, and 76 workers were killed during the construction. Their average age was just 21.

With the Wu River flowing in front of it and the towering Wuling Mountain standing behind, the plant is said to be situated in an 'extremely secretive' location. The enormous space spans more than 12 miles, with 18 main caves and more than 130 roads and tunnels, which vehicles are free to pass through.

The largest cave is 261 feet in height. The hollow is believed to be the world's largest man-made cave.

In order to prevent Soviet intelligence from tracking down the facility, China erased Bailang Town from every single map for nearly two decades.

Beijing had actually intended the 816 Nuclear Military Plant to be a back-up project for its main nuclear factory, known by its code name 404.

According to the New York Times, the 816 facility was meant to be an underground replica of the 404 plant.

The construction of the Bailang Town plant was called off in 1984 due to a change in national strategies. It was close to completion at that stage.

The base wasn't declassified until April 2002 and was only turned into a tourist attraction lit by neon lights in 2016.

Most of the factory's originally structure and equipment, which include the most advanced computer in China at the time, have been kept for tourists to view.

An administrator at the facility told China Daily that it is radiation free and open to foreign visitors. He added that the tour of the site takes three hours.