...in southern Norway just at the Swedish border.
It's best to get to feredriksten from Norwegian capital of Oslo by train or Swedish Gothenburg city on a fast train. From Gothenburg it will be a little longer, and for the money, oddly the same. From Oslo it is 1 hour 40 minutes for 250 crowns. From Gothenburg it costs the same money, for a little more than 2 hours trip. Tickets and schedule can be seen here: www.nsb.no.
The border there is generally invisible, unless you smugle to Norway a voluminous trunk with liquor (it a little bit cheaper in Sweden). Then, on the border you will be seized and detained in full accordance with the strict Norwegian customs legislation. Well, and then - goodbye Shangen's visa or permanent residence for many years ...
Arriving at the border town of Halden, the first thing you walk in the near r/w station pub 'Siste Reis', drink beer there, and then go out, turn to the left and see the fortress on the hill. If you do not see any fortress on the hill, that's mean you are either turned to the right, or you fаll and lie face down in a ditch. In this case, you'll have to postpone a visit to the fortress probably until next time ...