Chelyabinsk is one of the most polluted places in the world. On 29 September 1957, an explosion ripped through the nearby Mayak nuclear plant — which processed plutonium for the Soviet Union’s atomic bombs — casting a cloud of highly radioactive debris across the central Russian region. Despite communist officials keeping the disaster tightly under wraps, tens of thousands of people were, eventually, evacuated from the worst-hit villages, and vast swathes of the surrounding area have been closed to the public.