The mighty Akershus fortress has protected Oslo from foreign invaders since the Middle Ages. Just minutes from the center of Oslo, this fortress offers beautiful views of the entire city. The castle also tells the history of Norway's war. It is worth noting that walking in the area is free, while entrance to the castle has a small fee. On the castle grounds, you'll also find museums of the Resistance and the Armed Forces. It is the perfect destination for all history and architecture lovers.