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For 17 years, China secretly excavated the world’s largest artificial cave — and then abandoned everything without explanation
In 1966, Premier Zhou Enlai personally approved a project that would be kept in absolute secrecy for four decades: the construction of an underground nuclear weapons factory inside a mountain in the Fuling region, today part of Chongqing.
According to documentation from the 816 Nuclear Military Plant, the project mobilized over 60,000 workers who toiled in secret for 17 years, excavating rock to create the world’s largest artificial underground structure.
However, in February 1984, when the work was 85% complete, the government simply canceled everything.
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Thus, billions of yuan and the sacrifice of thousands of workers resulted in a gigantic cave that never fulfilled its purpose — just like the Yucca Mountain nuclear waste repository in the United States, which also cost billions and never received a single barrel of waste.
Furthermore, the project remained classified until 2002 and was only opened to the public in 2010.
The absurd numbers: 20 km of tunnels, 13 levels, 79 meters high, and 80 underground roads
The total surface area of the caves exceeds 104,000 square meters — more than 10 football fields excavated within solid rock.
Consequently, the complex is recognized as the world’s largest artificial underground structure.
Furthermore, the interior has 13 levels, 18 interconnected caves, 80 internal roads, and 130 connecting tunnels.
Similarly, the main cave — where the reactor would have been installed — is 79.6 meters high, equivalent to a 20-story building completely underground.
To put it in context, if the main cave were a building on the surface, it would be taller than most commercial buildings in the city that literally sits above it.
Likewise, the total length of all tunnels combined exceeds 20 kilometers — the distance of an entire half-marathon drilled inside a mountain.
In this sense, the 60,000 workers excavated over 17 years the equivalent of removing an entire mountain from the inside out — and then left the hole empty.
The fear that created the cave: when China believed the USSR could invade it at any moment
Project 816 was born in the context of the Third Front — a defensive industrialization campaign launched by Mao Zedong in the 1960s.
According to Atlas Obscura, the Third Front envisioned the transfer of strategic industries from the Chinese coast to the mountainous interior — away from Soviet or American bombings.
Therefore, excavating a nuclear factory inside a mountain was military survival doctrine, not eccentricity.
However, Sino-Soviet relations improved in the 1980s, and the threat disappeared.
As a result, in 1984 Deng Xiaoping decided to cancel the project — prioritizing economic development over nuclear paranoia.
Still, the project remained a secret for another 18 years — the residents of Fuling did not know what existed beneath their mountains.
Above all, the cancellation when only 15% remained for completion makes 816 even more surreal: China invested 17 years to create something it abandoned in the final stretch.
60,000 workers who couldn’t tell anyone what they were doing — for almost two decades
The workers lived in militarized camps around the mountain, without contact with the outside world.
According to Young Pioneer Tours, the workers were forbidden from revealing any details — even to family members.
Furthermore, conditions were extremely dangerous: manual excavation in hard rock, poor ventilation, and a constant risk of collapse.
In fact, it is estimated that dozens died during construction — although official numbers have never been released.
Consequently, 816 is both an engineering feat and a memorial to the human cost of the Cold War arms race.
On the other hand, many of the survivors could only tell their stories after declassification in 2002 — almost 40 years after they started working.
Today visitors walk through nuclear tunnels that never saw uranium
In 2010, the cave was opened as a tourist attraction — 26 years after its cancellation.
Only a fraction of the 20 km is accessible, but what is open already causes astonishment: enormous corridors, chambers that resemble underground cathedrals, and equipment that was never used.
Despite this, the site receives thousands of tourists seeking the experience of walking inside an abandoned nuclear weapons factory.
China spent 17 years, mobilized 60,000 workers, excavated 20 km of tunnels, and created the largest artificial cave in history — all to manufacture nuclear weapons that were never manufactured, inside a facility that never functioned, in a project that no one was supposed to know existed.
Project 816 is definitive proof that, in the Cold War arms race, fear was capable of moving mountains — literally. And that sometimes the most impressive story is that of the project that never happened.
816 in the context of underground megaprojects: larger than CERN and more secret than Cheyenne Mountain
To grasp the scale of Project 816, it’s worth comparing it with other famous underground projects.
Furthermore, the Large Hadron Collider (LHC) at CERN, Switzerland, has a 27 km underground circumference — but it is a narrow circular tunnel, not a 13-level complex with 18 caves.
Similarly, Cheyenne Mountain in the USA, the famous NORAD headquarters, has approximately 2 km of tunnels — ten times less than 816.
Consequently, Project 816 remains unparalleled in scale: no other artificial underground structure in the world combines 20 km of tunnels, 13 levels, and an 80-meter-high cave in a single complex.
Above all, the crucial difference is that both the LHC and Cheyenne Mountain are fully operational — while 816 was abandoned without ever having functioned.
Likewise, the history of 816 finds parallels in other canceled Cold War megaprojects: the USA also abandoned monumental nuclear projects, such as the Clinch River reactor, canceled in 1983 after US$1.7 billion invested.
Therefore, Project 816 is not just a Chinese curiosity — it is a universal phenomenon of the Cold War, when nuclear fear motivated colossal investments in projects that peace rendered unnecessary.
However, 816 stands out for its absurd scale and for having been kept in absolute secrecy for 36 years — a secret that 60,000 people kept for their entire lives.
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