Cloud Gate (The Bean)

Cloud Gate is a 110-ton drop of liquid mercury that someone forgot to clean up in Millennium Park — at least that's what it looks like. Anish Kapoor's stainless steel sculpture, universally known as the Bean despite the artist's objections, has been Chicago's most photographed object since it was unveiled in 2004, and the engineering behind it is as impressive as the aesthetics.

The sculpture is made of 168 stainless steel plates welded together and polished until the seams disappeared, creating a mirror surface that reflects the Chicago skyline from every angle. Stand back and you see the city's towers bending and warping across its surface like a funhouse mirror version of the lakefront. Walk underneath and you're inside the 'omphalos' — a concave chamber where your reflection multiplies and distorts in patterns that have kept children and adults equally fascinated for two decades.

The practical genius of the Bean is that it works at every scale. From across the park, it's a landmark. From 20 feet away, it's a mirror that puts you inside the skyline. From directly underneath, it's an optical toy that makes everyone look ridiculous in exactly the same way, which turns out to be an excellent social equaliser. On a summer evening, when the setting sun turns the western face gold and the city lights begin to appear in the eastern reflection, it's genuinely one of the most beautiful public artworks in America.