Tourists paying a visit in Chongqing, China, may now add the underground nuclear base 816 Nuclear Military Plant, which used to be a top-secret military location, in their itineraries.

After more than a year of undergoing some renovations, the 816 Nuclear Military Plant has now been reopened to the public, and foreign visitors are welcome.

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Modifications included installing new sound and lighting effects along its corridors, putting up a nuclear science center, and opening other restricted sections, making the site a perfect avenue of integrating history and modern technologies, China Daily reported.

Furthermore, the 2001 process pipelines in the nuclear reactor have also been restored, which are designed to demonstrate the nuclear fission process via photoelectric effect, People's Daily China noted.

The abandoned nuclear plant has been dubbed as the biggest artificial cave in the world at a size of 1.1 million square feet (that is apparently the size of 20 football fields). Visitors could enjoy more than 12 miles of caves with over 130 different roads, tunnels, and shafts to explore through. The largest cave is the nuclear reactor hall with a height of 262 feet and width of 82 feet, according to Daily Mail.

The 816 Nuclear Military Plant used to be the nuclear engineering site of the country that could withstand thousands of tons of explosives and even an 8.0 magnitude earthquake. It used to be highly confidential military site in the mountainous town of Baitao in Fuling District.

Construction of the nuclear plant began in 1966 but was halted by the Central Military Commission in 1984 because the world's situation was relatively peaceful, People's Daily China reported.

The base was first opened to the public in 2010 for Chinese visitors. With an investment of 60 million yuan ($9 million), the plant underwent a facelift in 2015 to ensure add safety and tourism features, according to South China Morning Post.

Meanwhile, tickets for the site cost 60 yuan ($9) during peak season (between April and October) and 45 yuan ($6.70) during off-season (November to March), Global Times noted.

Here's a virtual tour:

Tags816 Nuclear Military Plant, nuclear plant, tourist attraction, china, Chongqing, military base