This ramarcable fort is located in southeastern Norway near the border with Sweden in Glomme river valley.
There is no problem, if you are already in Norway capital Oslo and not far from the Central railway station. All you need is get to that station, buy a ticket on the train to the town of Mysen (45-50 min), take this train and go.
Generally there is no public transportation from Mysen reailway station to the fort. You can of course book a taxi but true sportsmen don't do so. All that remains is to move by the foot in NE direction to the fort about 4.5 km. accordingly to the attached map. Well, good luck, comrade!