For 14 years, Snøhetta’s gleaming Oslo Opera House, with its walkable roofs of white Carrara marble, has dominated the cultural district where Oslo meets its namesake fjord. The architects of the city’s new central library, immediately inland from the opera, might have created a self-effacing building, rather than risk upstaging an icon. Instead, they turned a competition stricture meant to permanently protect views of the opera from the city’s central train station into a source of inspiration. The partnership of Atelier Oslo and Lundhagem angled their building away from the opera, leaving the sightlines from the station undisturbed, until it reaches about 60 feet in elevation, too high to block Snøhetta’s low-lying structure. At that point, the library’s 24-foot-high top floor cantilevers dramatically into the viewshed, from some angles appearing to fill a void created by the opera’s irregular roofline.