This Denver art museum, which opens this fall, is devoted to the work of the late abstract expressionist Clyfford Still. The architects designed a two-story, 28,500-square-foot concrete structure. They chose the material for “its weight—it has a mineral quality,” says principal Brad Cloepfil, AIA. A porous concrete ceiling admits diffuse light into the galleries; trees screen the façades. A low entrance canopy leads to a 150-foot-long lobby with 10-foot ceilings. “It’s a preparatory experience, stripping you down,” Cloepfil explains.