The sculpture is actually entitled, "Cloud Gate." It is the centerpiece of Millennium Park in Chicago. Made up of 168 stainless steel plates welded together, its highly polished exterior has no visible seams. It is 33 by 66 by 42 feet (10 by 20 by 13 m), and weighs 110 short tons.
Said to have been inspired by liquid mercury, the sculpture's surface reflects and distorts the city's skyline. Visitors are able to walk around and under Cloud Gate's 12-foot (3.7 m) high arch. On the underside is the "omphalos" (Greek for "navel"), a concave chamber that warps and multiplies reflections. The sculpture builds upon many of Kapoor's artistic themes, and is popular with tourists as a photo-taking opportunity for its unique reflective properties.
The sculpture was selected during a design competition. After Kapoor's design was chosen, numerous technological concerns regarding the design's construction and assembly arose, in addition to concerns regarding the sculpture's upkeep and maintenance. Various experts were consulted, some of whom believed the design could not be implemented. Eventually, a feasible method was found, but the sculpture's construction fell behind schedule. It was unveiled in an incomplete form during the Millennium Park grand opening celebration in 2004, before being concealed again while it was completed. Cloud Gate was formally dedicated on May 15, 2006, and has since gained considerable popularity, both domestically and internationally.