The technique of hanging an artwork, typically sculptural, from the ceiling, or suspending a series of objects in space, giving the effect of them floating in air. The development of the technique is linked with a number of different modernist avant-garde practices: Marcel Duchamp hung readymades such as a shovel and hat rack from the ceiling, while Alexander Calder's iconic mobiles were delicate "drawings in space" susceptible to subtle movements of air. Playing with concepts of visual perception and interactivity, Jesús Rafael Soto's Penetrables consist of thin hanging tubes that permit viewers to enter the space of the sculpture itself. The hanging of objects from above has become common in contemporary installations, especially in works that seek to create an immersive or engineered effect. These range from Ernesto Neto's membrane-like passageways, to Cai Guo-Qiang's dramatic installations, to Maurizio Cattelan's humorous, provocative sculptures, all of which were hung together in the Solomon R. Guggenheim Museum's rotunda for his retrospective exhibition, "All."