Viennese architect Silja Tillner has designed a delicate retractable canopy for the Vienna City Hall courtyard that respects the historic building it covers. When the canopy is fully extended, the accordion-folds provide numerous ridges and valleys that collect rainwater. To drain the water properly, the architect, with engineers Schlaich Bergermann und Partner, developed this simple but effective drainage device. At both ends of each valley, a flexible wedge-shaped fabric cant directs water away from the ends toward the drains. The drains are fitted with fabric tubes (with metal chains down their centers) that extend to the ground and control runoff. They serve a practical purpose as well as act as visual supports for the delicate white canopy against the backdrop of the dark stone façade of the courtyard.