Viennese architect Coop Himmelb(l)au has won an international design competition for the £100m headquarters of the European Central Bank in Frankfurt.

In the winning design, twin 40-storey towers are connected by an atrium conceived of as a "vertical city" of hanging gardens, cafeterias and lounges. It is criss-crossed by numerous stairs and ramps between the towers. The atrium and towers will rely largely on natural ventilation designed by Arup. Bollinger + Grohmann of Frankfurt is structural engineer and Letzbor Bauengineering of Vienna is cost consultant.