Photo: Wikimedia CommonsThe Oslo Opera House rises from the Bjorvika waterfront like a slab of drifting ice, and its great sloping roof of white marble and granite is open for anyone to walk right up. Climbing to the top for the sweep of fjord and city costs nothing and is one of the essential Oslo experiences, day or night. Time it for sunset, wear sensible shoes for the angled stone, and peek inside at the wave-like oak walls of the foyer while you are there.