Zheleznogorsk (Russian: Железного́рск) is a closed town in Krasnoyarsk Krai, Russia, with a developed nuclear industry. It was a secret city, established in 1950 for the purpose of researching nuclear weaponry and producing massive quantities of plutonium, the facilities for which were hidden inside a hollowed-out mountain. It appeared on no maps, and had no census data. Although more than 100,000 people lived there at one point, satellite imagery would have shown only a fairly small mining town. The mountain complex contained 3,500 rooms and three plutonium reactors. The space had been excavated by tens of thousands of gulag slave laborers, who removed more rock from inside the mountain than was used to build the Great Pyramids. Protected under the granite peak of the mountain, these facilities would survive a direct nuclear attack.
No one called it “Zheleznogorsk.” Officially, it was “Krasnoyarsk-26,” which is something like naming a city ‘Arizona-17.’ Residents traveling outside the city called it Iron Town, if they had to refer to it at all. They were under strict instructions never to reveal to anyone the actual business of Krasnoyarsk-26. As is the tradition with Soviet towns containing secret facilities, "Krasnoyarsk-26" is actually a P.O. Box number and implies that the place is located some distance from the city of Krasnoyarsk. The town was also known as Soctown, Iron City, the Nine, and Atom Town.
And life there was amazing. People living and working in the secret city received some of the best wages in the Soviet Union. There were sports stadiums, public gardens, a movie theater, and the shortages notorious in the rest of the USSR were unknown. The best nuclear scientists in Russia lived in a sealed-off utopia. A third of all the nuclear weapons produced in Russia during the Cold War were powered by fuel from Zheleznogorsk.
Their flag and coat of arms is a bear splitting the atom: