Chongqing, China (CNN) — The tunnel darkens beneath eerie red and blue lights, the only beacons in the otherwise black surroundings. The cave's air is chilly, rich with the odor of dust and freshly washed concrete.
Pressing past a giant People's Liberation Army green iron door, a concrete cavern the size of a football field opens up in China.
One wall, stretching over a hundred feet high, displays neon lit movie panels with images of atomic weapons and plutonium processing.
Across the hall, another wall displays a fiery orange atomic mushroom cloud.
Beneath this mock Armageddon is a field of sand filled with miniature Chinese army trucks and a life-size replica of China's first atomic bomb, which was detonated during a nuclear test in 1964.
In front of it all, Chinese families and friends stop and pose for photos and selfies.
Welcome to the belly of China 816 Nuclear Military Plant, a decommissioned Cold War-era plutonium and weapons processing facility buried in the Chongqing mountains that contains one of the world's largest man-made caves.
Nuclear spelunking in Chongqing: A colorful experience.
Construction commenced in 1967. According to government figures, more than 60,000 soldiers worked on it for 17 years before it was shut down in 1984. It opened for the Chinese public briefly in 2010 but was closed shortly after.
The 104,000 square meter facility, filled with 18 caves and 130 tunnel roads, recently opened again -- this time as a tourist destination accessible to international visitors.
Past the nuclear bomb display hall visitors make their way through a tubular tunnel rimmed with blue, red, and green lights, which project onto the walls for stunning visual effects.
Out of this corridor lies a warren of concrete rooms bathed in orange, blue and green hues. Ascending staircases lead to rooms with reactor meters and Cold War-era history displays.
Avant-garde green lighting in several areas highlights where radioactive processing occurred.
Anything that might have been radioactive is encased in protective glass. Other rooms are lit by simple lights, exposing original white and blue walls and tiles. There are deep, dark gaps with exposed wrought iron, and vast areas with rooms that are off limits.
Not that they need to be marked -- even the most curious Dungeons and Dragons enthusiast would be terrified to start idly poking around 816.
Red books and gas masks
The latter third of the tour takes visitors into a labyrinth of concrete rooms lit with sci-fi-like light displays.
Plaques note heroic engineering and Cold War, Chinese communist lore, while one room features a glass box with Chairman Mao red books and nuclear gas mask and fallout body garb.
Another sprawling room contains a depression the size of an Olympic swimming pool.
The former nuclear bunker is filled with rooms highlighting the site's work.
An art installation of plastic tubes sprouts up from this basin in lime green, representing the nuclear rods once housed here.
Above this, once sterile walls bleed with rust. Corroding staircases dangle off them. Final halls resemble fabled mines with 200-foot ceilings cut out of rock and lit with white lights.
One room offers overhead views into a sort of mad science lab, its ghoulish green lights shooting up through the glass floor.
An exhilarating and refreshing tour
Only a third of 816 is currently open, with other areas of the mountain still highly restricted to tourists.
Officials are planning to open other sections in the future.
But what is on offer during the two-hour exploration is already enough, making 816 an exhilarating and refreshing experience.
It combines interesting science and dramatic history with the thankful sentiment (if set in a deeply Chinese patriotic language) that the Cold War is over.
Given the edgy lighting and space design, one might imagine 816 transforming into the largest underground nightclub on Earth. Until then, it will have to settle for being the coolest nuclear bunker spelunking site there is -- no serious cave exploring gear required.
Thirty minutes by train from downtown Chongqing and one hour drive into Fulin county, 816 rests in the hills that overlook the Wu River, a southern tributary of the Yangtze that flows down to Guizhou.
Located in southwestern China, Chongqing -- often referred to as "River Town" -- is the country's largest municipality. It's home to over 30 million people -- 10 to 12 million bustling around its multiple riverfront downtown and 18 million or more peppered across rolling hills and mountains that abut the Qinghai-Tibetan Plateau.
The 816 bunker complex is one of several destinations Chongqing tourism authorities have dubbed "cave cool."
Famed for its inferno-on-the-tongue peppercorn hot pot cuisine, the province is also legendary for caves owing to the ancient Yangtze river and karst limestone geology.
These caves form an essential element of Chongqing's culture and history -- with some of the most popular ones being refurbished into entertainment, dining, and tourist attractions.
Others have been preserved for scientific research only.
This story was originally published in October 2016.