First Sears sold the building and moved to cheaper suburban offices in 1992. Next, the Petronas Towers in Kuala Lumpur, Malaysia, claimed the title of world's tallest building, followed by the Burj Khalifa in Dubai. Then came the final blow: In 2009, this iconic landmark was officially renamed Willis Tower, after the international insurance company that became its main tenant. Real-estate deals aside, Chicagoans stubbornly insist on calling it the Sears Tower, so feel free to do so as well.

Despite the fact that this observation area on the 103rd floor is called a "skydeck," you can't actually walk outside, but the panoramas are impressive nonetheless: On a clear day, visibility extends up to 50 miles and you can catch glimpses of four surrounding states. The most nerve-wracking viewing spot is the Ledge, a series of clear observation boxes that jut out from the side of the building: Step out, and there's nothing between you and the ground but a layer of see-through glass. Inside the Skydeck, multimedia exhibits on Chicago history and Knee High Chicago, an exhibit for kids, add some perspective to what you're seeing outside. Be forewarned that in the summer you may be stuck in a very long, very noisy line in the lobby, so by the time you make it to the top, your patience could be as thin as the atmosphere up there. (Come in the late afternoon or early evening to avoid most of the crowds.) The 70-second high-speed elevator trip will feel like a thrill ride for some, but it's a nightmare for anyone with even mild claustrophobia. Allow 1 hour, more if there's a long line.