Rjukan–Notodden Industrial Heritage Site is a World Heritage Site in Telemark county, Norway, created to protect the industrial landscape around Lake Heddalsvatnet. The landscape is centered on the plant built by the Norsk Hydro to produce fertilizer from atmospheric nitrogen. The complex also includes hydroelectric power plants, transport systems, including railways, transmission lines and factories, and workers' accommodation and social institutions in the towns of Notodden and Rjukan.