Out on the vast plains of the Kazakh steppe lies a place with an eerie secret. Covering an 18,500 square km stretch of wilderness, it looks to all intents and purposes like just another swathe of endless grassland. Yet this quiet exterior hides a sinister past. During the years of the Soviet Union, this area was strictly off-limits.Those who could get close enough witnessed blinding flashes, watched in awe as mushroom clouds expanded across the sky. This place’s name was the Semipalatinsk test site, also known as the Polygon. Today, we know it as the most-nuked place on Earth.