Known as the largest man-made cave in the world, the 816 Nuclear Military Plant, is located in the mountains of Fuling district in China's Chongqing municipality.

This former top-secret nuclear military plant was once used to manufacture plutonium and house thousands of explosives. Recently, it has been re-opened to tourists and visitors for the first time.

The underground military plant, located in the mountains of central China, is almost 20km wide, and includes 178 man-made caves and over 130 roads and tunnels.

It includes 18 caverns, the largest of which is about 80 meters high. It was designed to tolerate thousands of tons of TNT explosives.

The facility, which was hidden in the mountains of Fuling, reportedly was the death place of 100 out of 60,000 engineering soldiers, who participated in the construction of the largest man-made cave ever created in the world.

The repaired 816 Nuclear Military Plant in Chongqing municipality was commissioned in the 1960s, after Beijing was fearful of an attack by the Soviet Union.

But in 1984, just before construction finished on the project, work was halted and the facility has never even used.

Accordingly, the area has remained off-limits to foreigners until now, with Chinese nationals being the only ones allowed to tour the facility since 2010.

As the former Nuclear Plant has been re-opened as tourist attraction, the experience is being advertised by China Tourism as the feeling of being in a science fiction film with some fancy lighting and sound installations.

According to Mr. Yang Yan, an administrator at the site, "A tour takes three hours. Visitors must follow the guide, otherwise they will get lost in this huge maze-like cave."

'This base has never been put into operation or stored any nuclear material. There is no need to worry about radiation. It is safe to enter,' he added.

These days, it's been renovated to feature colorful modern lighting, as well as educational displays. The administrator advised that visitors need not fear for their safety.