NEW YORK CITY—New York City's newest cultural center, the Shed, opens on April 5. It's topped with an ETFE polymer (translucent plastic) shell supported by a steel frame that glides along a track on wheels. The hood can slide in a telescopic way to expand, contract and create an open-air amphitheater space. The structure resembles a gigantic, Space Age Conestoga wagon for pioneers of the arts to travel into the future.