A curving ladder of sculptural balconies rises above the double-height display windows of UNStudio’s first project in Brussels—a mixed-use block on the highend Avenue de la Toison d’Or. Situated between the historic gates Porte Louise and Port de Namur, the structure’s organic lines “echo a quality we find in Victor Horta’s work and other Art Nouveau architects from the turn of the century,” says principal Ben van Berkel.

But, belying its vintage influences, the building, clad in glass-fiber reinforced concrete panels, is thoroughly modern in construction and amenities, with an elevated garden, triple glazing for the windows, and a cogeneration system that supplies heating, cooling, and warm water to the 72 apartments and to 130,000 square feet of retail space, while also sending electricity to the grid. UNStudio aimed to make the street-level boutiques open and light, contrasting with “the apparent solidity of the upper floors,” van Berkel says, “to create the illusion that the vertical, balloon-like frames were carrying the building.”