The facade of the new building for the Kunstmuseum Basel produces its effect through the symbiosis of stone and light: a three-metre-high frieze encircles the building at a height of twelve metres. Its horizontal joints are cast in shadow by the incident daylight. White LEDs are set into the joints so they cannot be seen from the street yet precisely illuminate the specially formed grooves. Reflection on the light-coloured bricks of the frieze creates an indirect light that can be used to display both text and graphics. The frieze was designed to be an integral part of the architecture. The subtle way it is enlivened by light allows the facade to change its character, seeming sometimes more and sometimes less transparent, and suggests diverse interactions between the building’s interior and the surrounding urban space. During the day, the brightness of the illuminated joints corresponds to that of the ambient light outside. For the viewer, a powerfully poetic play of light and shadow emerges, which is fleeting and yet seems to be as solid as the masonry itself. As daylight fades, the frieze adapts to the new environmental conditions, becoming more radiant.