Akershus Fortress (c 1300) faces the sea in defiance of any attempt to invade from the water. It was transformed into a Renaissance palace by Christian IV in the early 17C. Nowadays it is used for official functions; in its grounds it also houses Norway's Resistance Museum, highlighting its role during the Second World War. Check out the ramparts, the fine panoramic view over the port, the fjord and the spectacle of the ships.