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Designed by the same team (Skidmore, Owings & Merrill) that designed the Willis (formerly Sears) Tower, this multiuse skyscraper is distinguished by its tapering shape and enormous X braces, which help stabilize its 100 stories. Soon after it went up in 1970, it earned the nickname "Big John." No wonder: it's 1,127 feet tall, 1,502 feet counting its antennae. Packed with retail space, parking, offices, a restaurant, and residences, it has been likened to a city within a city. It's impressive from any angle and offers mind-boggling views from a 94th-floor observatory, where, like the Willis Tower, you can see to four states on clear days. Those with vertigo might prefer a seat in the Lavazza Espression Café or the bar of the 95th-floor Signature Room. The tab will be steep, but you don't pay the observatory fee and you'll be steady on your feet—maybe.