Photo: Wikimedia CommonsGuarding the harbour since around 1300, Akershus Fortress is a medieval castle turned royal residence whose ramparts give some of the finest free views over Oslo and the fjord. You can roam the grassy grounds and cobbled lanes without a ticket, watch the changing of the guard, and look in on the on-site museums if you wish. Wander up in the late afternoon for golden light on the walls, and follow the battlements around for the best angles on Aker Brygge below.