Akershus Slott & Festning

Akershus is the old castle built to protect Oslo which has also been used as prison. The first work on the castle started around the late 1290s, by King Håkon 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.

Akershus has never been successfully captured by a foreign enemy. The fortress has successfully survived many sieges, primarily by Swedish forces. In the early 17th century, the fortress was modernized and remodeled under the reign of the active King Christian IV, and got the appearance of a renaissance castle. The fortress was first used in a battle in 1308, when it was besieged by the Swedish. It was strategically important for the capital, and therefore for Norway as well. Whoever ruled Akershus fortress ruled Norway.

Akershus fortress is still a military area, but is open to the public daily until 9pm. In addition to the castle, the Norwegian Armed Forces museum and the Norwegian Resistance museum can be visited there. The Norwegian Ministry of Defence and Defence Staff Norway (armed forces headquarters) have a joint modern headquarter in the eastern part of Akershus Fortress.

Furthermore, Norwegian Royalty have been buried in the Royal Mausoleum in the castle.