Designed by Diller Scofidio + Renfro, the Hirshhorn Museum is a 145-foot-tall inflatable meeting hall that seems to float in the sky, for it features a large translucent fabric bubble on top of its internal courtyard to create an air of lightness. Stabilized by an enormous tube of water which surrounds the interior structure, the museum bubble gets strength from a series of large steel cables tethered to the inner tube at one end and the roof-level truss on the other. Installed twice a year, in May and October, the balloon structure will add additional space to the main hall in a very short period. Visitors will be able to access the bubble through a short, tube-shaped corridor installed between the lounge and central courtyard of the museum. Costing about $5 million, the translucent blue facade lets the visitors peep into the mall.