Between 1949 and 1989, 456 nuclear tests were conducted on the territory of the Polygon, the Soviet Union's primary nuclear test site, both above and below ground. Much of the 18,000 sq km area is now considered safe to visit and you can do so with a guide and car organised by the National Nuclear Centre (easiest via tour agency) in Kurchatov. Radiation suits are dished out for visiting the parts where the radiation levels are considered to be dangerous.
In the desolate steppe, the tour allows you to explore the ruins of watchtowers, some underground bunkers, and even the remains of a metro. You can also expect to see sites such as the Opytnoe Pole (location of the first nuclear test), the 'Atomic Lake' (a water-filled bomb crater created as an experiment in 'peaceful' landscape change) and the Degelen Mountains, where bombs were exploded in tunnels cut into hillsides. Your guide carries with you a Geiger counter to demonstrate the levels of background radiation in the town of Kurchatov, comparing them to the different parts of the Polygon.