Rjukan is the centre of the municipality Tinn in Telemark with approximately 4000 inhabitants.

Established from 1907—1916 when Norwegian Hydro started their saltpeter production there because Rjukanfossen, a 104 metre waterfall, provided easy access to a lot of electricity. It was also the location of a supply of heavy water during World War II for Nazi Germany, which investigated the possibility of building an atomic bomb. This lead the Allies to sabotage the heavy water production.