A very Soviet phenomenon, but one still existing in modern Russia, although many cities are now "open". Known as ZATO (zakrytye administrativno-territorial'nye obrazovaniia) in Russian. Appeared from the late 1940s onwards. Note that living there was not necessarily bad - it involved (and to a lesser extent, still involves) reasonably good and prestigious if secret work, lots of cool if sometimes dangerous stuff happening, and various privileges such as a temporary exemption of local businesses from taxes in the Nineties.