The greatest world’s fair to date welcomes its visitors with an impressive symbol – the central Expo Axis with its unique roof construction. The 1 km long and 100 m wide Expo Axis features pedestrian areas on four levels and is covered by a 65,000 m² membrane roof supported by 19 interior columns, 31 exterior pylons, and 6 funnel-shaped elements made of steel and glass with a doubly curved freeform frame structure. The so-called ‘Sun Valleys’ introduce daylight into the levels below and provide orientation within the huge complex. The concept of a built landscape with flowing transitions between interior and exterior called for a roof construction that expressively symbolises openness.