And the reason it was built so deep underground? It was designed to withstand a nuclear bomb.
Olga Arkharova, the director of the bunker's museum, says the vast dugout fell into disrepair during the economic chaos of the 1990s. Today, ground water is seeping in through the concrete and there is an overbearing smell of rust and mold.
But last year, the bunker was auctioned off to a private company, which intends to give it a new lease on life. The plan is to turn it into an underground leisure complex and hotel, complete with shops and a spa.
"The necessity to put things underground is obvious," says Nikolai Temerev, the general director of Novik-Serviz, the bunker's new owner. "There are big problems in this city -- transport problems, communications problems. And these need to be resolved.
"Either we can build upwards -- like, say, in Japan, where they have all these overpasses. But that would mean covering the landscape with triple-level roads. The other option is to build underground. And in that way you don't change the face of Moscow, which is of historical importance to the city and to the Russian people."
With an estimated 13 million residents, Moscow is Europe's most populous city -- and one of the most crowded. It's two-thirds the size of London, but with almost two times the population.
The Russian capital has seen a building boom over the last decade to cope with the explosion. But with space above ground fast running out, city planners are starting to build downwards.
Yury Luzhkov, the mayor of Moscow, has complained that only 8 percent of the ground beneath the city is currently being used. Over the next 10 years, he says, he wants to develop as much as a quarter of underground Moscow. He has already set aside 25 plots below the city for major construction work.
Aleksandr Alyokhin, a spokesman for the construction department at City Hall, says planners are exercising caution in where they choose to dig.
"We're not planning to build everywhere beneath the city. The places we are developing have been chosen on a geological basis," Alyokhin says. "So wherever we can build, we will. But where the ground doesn't allow us to, where there are cables, for example, or where there are underground rivers, we won't build there. It'll all be done according to the geological map of underground Moscow, which is soon going to become available."
Constructive, Or Destructive?
Alyokhin says the construction projects include entertainment centers, underground car parks, and shopping malls. "Naturally, the only thing there won't be is people living down there," he adds. "The things we build will be infrastructure only."
Already, you can shop underneath Red Square, park your car five floors beneath street level and even take aerobics classes in an underground gym. All the same, some Muscovites are skeptical about the idea of building underground.
In February, traffic came to a standsill after a 120-square-meter sinkhole appeared in a roadway in western Moscow.
"I'm not sure it's a good decision," said one shopper at the Manezh center, a three-story underground mall just beyond the Kremlin walls. "We don't need many more stories to be built under Moscow, because it will just destroy the city. Russians should develop other cities or towns, not only Moscow. Russia isn't only Moscow."
Others have warned that the current flurry of underground construction work could cause the city to cave in if it is not rigorously monitored.
"It's understandable that they should want to look for what they can do underground. But there are issues, problems with instability," says Edmund Harris, a spokesman for the Moscow Architecture Preservation Society. "There are areas in Moscow which are geologically dodgy, so they need to proceed very carefully. I think my main worry would simply be that they don't yield to pressure from developers and investors to do everything as quickly as possible."
One of Moscow's main thoroughfares, Leningradsky Prospekt, last year partly caved in, an incident blamed on nearby construction work. In February, traffic came to a standstill after a 120-square-meter sinkhole appeared in a roadway in western Moscow. And a square in the city center collapsed on April 22 after construction workers hit an underground stream.
But back at the Stalin-era bunker, construction work is in full flow.
"Our idea, our plan is to turn the whole thing into an exhibition center and leisure complex," says Olga Arkharova. "And we'll also have a restaurant here. Not just any old restaurant -- it will be a military-style canteen."
And if the mayor of Moscow gets his way, within a decade there will be dozen more restaurants, cafes, shopping centers, and even roads -- in what is fast becoming a city beneath a city.