Willis (Sears) Tower
Once the world’s tallest building, Willis Tower (formerly known as Sears Tower) is still the USA's tallest building, and it's still way up in the clouds. Its observation platform - the Skydeck - draws 1.5 million people a year who are eager to ascend the 110-story, 1,454 foot (443 meter) building for awesome panoramic views of the city and surrounding countryside.
Your journey to the top of the Willis Tower starts with a walk through an airport-style metal detector, followed by a slow elevator ride down to the waiting area where visitors queue for tickets. A sign will tell you how long you'll have to wait to get up high; this is a good time to confirm the visibility. Even days that seem sunny can have upper-level haze that limits the view. On good days, however, you can see for 40 to 50 miles (64 to 80 kilometers), as far as the states of Indiana, Michigan. Iowa, and Wisconsin.
While you wait, you can watch a film about Willis Tower factoids like its 43,000 mi (69,200 km) of phone cable and 2,232 steps to the roof. Then you'll wait a little longer before the ear-popping, 70 second elevator ride up to the 103rd floor deck. From here, the entire city stretches below, and you can see exactly how Chicago is laid out.