At fifty-three storeys, the Commerzbank is the world's first ecological office tower and the tallest building in Europe. The project explores the nature of the office environment, developing new ideas for its ecology and working patterns. Central to this concept is a reliance on natural systems of lighting and ventilation. Every office is daylit and has openable windows, allowing the occupants to control their own environment. The result is energy consumption levels equivalent to half those of conventional office towers.