The castle is free and open on the edge of Cape Ak. It's quite large, but it can't be entered. There is also a restaurant area beside the sea, which is very pleasant. Wide view, overlooking the city hall and downtown Oslo, magnificent. There are many cannons beside the waterfront wall. King Yukang V of Norway, designed and built in 1300 to resist foreign aggression, is one of the most representative buildings in the Middle Ages. This is my favorite building in Oslo, full of functional, artistic, obvious European architectural style, medieval history.