Nearly 40 years ago, something happened in the quiet, unremarkable coal-mining town of Yunokomunarivsk in the central Donbas that made it the subject of urban legends.

On Sept. 16, 1979, the Soviet authorities detonated a nuclear bomb inside the “Yuniy Kommunar” (“Young Communard”) coal mine, at a depth of 903 meters, just beneath the town of some 22,000 people.