Cloud Gate is British artist Anish Kapoor's first public outdoor work installed in the United States. The 110-ton elliptical sculpture is forged of a seamless series of highly polished stainless steel plates, which reflect the city's famous skyline and the clouds above. A 12-foot-high arch provides a "gate" to the concave chamber beneath the sculpture, inviting visitors to touch its mirror-like surface and see their image reflected back from a variety of perspectives.

Inspired by liquid mercury, the sculpture is among the largest of its kind in the world, measuring 66-feet long by 33-feet high. Cloud Gate sits upon the At&T Plaza, which was made possible by a gift from AT&T.

From http://www.millenniumpark.org/artandarchitecture/cloud_gate.html