The Semipalatinsk Test Site — known to everyone simply as "The Polygon" — lies about 150 km west of the city and covers 18,000 km², roughly the size of Wales. Between 1949 and 1989 the Soviet Union detonated 456 nuclear devices here: 116 in the atmosphere and 340 underground. The first Soviet atomic bomb, codenamed RDS-1, was tested here on 29 August 1949. The human cost was catastrophic. Hundreds of thousands of people living in the surrounding steppe were exposed to radiation, with elevated rates of cancer, birth defects, and premature death persisting for generations.
The site closed in 1991 following a sustained campaign by Kazakh activists, and is now considered the best-researched nuclear testing site in the world — and the only one open to the public year-round. Visiting requires a permit and a guide arranged in advance; day trips from Semey are the norm. Ground zero areas, test shafts, and equipment abandoned mid-experiment are visible across the landscape. The scale and silence of the steppe amplify the weight of what happened here.