When designing a new regional headquarters in Copenhagen for the United Nations, the Danish architecture firm 3XN had to balance the need for security with an atmosphere of social engagement. So although the structure is isolated on a man-made island, a sense of openness and exchange prevails throughout its floor plan, which extends out, starlike, in eight wings, reflecting the organization’s broad reach. But the building’s communal spirit is perhaps most dramatically expressed in its six-story central atrium. Here, a sculptural network of elevated walkways and curving stairs—all clad in glossy black steel—facilitates movement around the complex and encourages chance encounters between colleagues.