Seven hundred years of fortification on a headland over the fjord, never taken by an enemy, and free to walk into.
Håkon V began building here around 1299, when he moved the capital from Bergen to Oslo, and the fortress has been continuously in military use ever since. It is still an army headquarters, which is why there are soldiers about and why parts of the site close without notice.
It has been besieged repeatedly — by the Swedes most often, including by Charles XII in 1716 — and it has never been taken by an attacking force. It was surrendered once, in 1940, without a shot.
The castle
Christian IV converted the medieval fortress into a Renaissance castle in the 1600s, which is essentially what you see: thick walls, small windows, and a courtyard.
Inside are the banqueting hall, the castle church, the dungeons, and the Royal Mausoleum — a stark modern crypt of 1948 holding the remains of Haakon VII and Olav V and their queens. It is severe, plain and moving, and it is the reason to pay the entrance fee.
The occupation
This is the difficult part of the site and Norway does not hide it.
The Germans occupied Akershus from 1940 to 1945 and used it as a prison and an execution ground. Members of the Norwegian resistance were shot here.
After the liberation, the fortress was used for the treason trials, and Vidkun Quisling — who had proclaimed himself head of government on the day of the invasion, and whose name entered English as a common noun for a collaborator — was executed by firing squad in the courtyard on 24 October 1945. So were several others.
There is a memorial at the execution site.
Norway’s Resistance Museum is inside the fortress walls and is the best account of the occupation anywhere in the country.
The grounds
Free, open long hours, and the best walk in central Oslo.
Ramparts, cannon, grass, and a view straight down the fjord past Aker Brygge to the islands. On a summer evening people sit on the walls with a bottle of something and watch the ferries.
There is a changing of the guard at the main gate, and the His Majesty The King’s Guard is based here.
Practical
The castle and the museums charge separately and have shorter, seasonal hours — winter opening is much reduced. Check before travelling for a specific building.
The grounds need no ticket at all.
Ten minutes on foot from the City Hall, or from Aker Brygge along the water.
More Landmarks
The Opera House
A building you are meant to walk on. The roof is a public square that rises out of the fjord, and it costs nothing.
Oslo City Hall
Two brown brick towers that Oslo has never entirely forgiven, and the room where the Nobel Peace Prize is awarded.
Holmenkollen
A ski jump at the end of a metro line, with the world's oldest ski museum inside the hill under it.