The Castle is part of the Akershus Fortress which is still used as a military installation...but is also open to the public daily from 6 am to 9 pm. Tours inside the castle however, seem to be limited to weekends. The best way to get a full view of the Fortress is from the harbor. There are also several museums and monuments here.
Wikipedia (
visit link) adds:
"...Akershus Castle (Norwegian: Akershus slott) is a medieval castle that was built to protect Oslo, the capital of Norway. It has also been used as a prison...
The first construction on the castle started around the late 1290s, by King Haakon V, replacing Tønsberg as one of the two most important Norwegian castles of the period (the other being Båhus). It was constructed in response to the Norwegian nobleman, Earl Alv Erlingsson of Sarpsborg’s earlier attack on Oslo...
The fortress has successfully survived all sieges, primarily by Swedish forces, also by Charles XII in 1716. In the early 17th century, the fortress was modernized and remodelled under the reign of the active King Christian IV, and got the appearance of a renaissance castle.
The fortress was first used in battle in 1308, when it was besieged by the Swedish duke Eric of Södermanland, whose brother won the Swedish throne in 1309. The immediate proximity of the sea was a key feature, for naval power was a vital military force as the majority of Norwegian commerce in that period was by sea. The fortress was strategically important for the capital, and therefore, Norway as well. Whoever ruled Akershus fortress ruled Norway.
The fortress has never been successfully captured by a foreign enemy. It surrendered without combat to Nazi Germany in 1940 when the Norwegian government evacuated the capital in the face of the unprovoked German assault on Denmark and Norway (see Operation Weserübung). During World War II, several people were executed here by the German occupiers. After the war, eight Norwegian traitors who had been tried for war crimes and sentenced to death were also executed at the fortress. Among those executed was Vidkun Quisling...
Norwegian Royalty have been buried in the Royal Mausoleum in the castle. They include King Sigurd I, King Haakon V, Queen Eufemia, King Haakon VII, Queen Maud, King Olav V and Crown Princess Märtha."