233 S Wacker Dr, Chicago, IL 60606, USA
Willis Tower—originally known as the Sears Tower—was the world’s tallest building for 23 years until it was unseated in 1996 by the Petronas Twin Towers in Kuala Lumpur. The 110-story skyscraper is still mighty impressive. Its “bundled tube” design by architectural firm Skidmore, Owings & Merrill was originally inspired by a handful of cigarettes and the innovative bundling changed the construction of supertall, wind-resistant buildings thereafter. The tower’s height is even more thrilling when measured from the 103rd-floor windows of the Skydeck observatory and the Ledge, a glass-enclosed box which juts more than four feet out from the side of the building so that visitors can (gingerly) walk out and stand 1,353 feet above the street.