The fortress was built in 1910 after gaining independence from Sweden to protect the road to Trondheim against a Swedish invasion.
However, it was not used until the Second World War against the attacking Wehrmacht. The Norwegian soldiers were able to move from 15.04. until May 5th, 1940, but then had to surrender to superior forces.
The rooms and corridors carved into the rock can be visited, but a headlamp is recommended as the rooms are not continuously lit.
The first two seasons of the Norwegian reality TV series "Norges tøffeste" were filmed in Hegra.