It's Chicago's tallest building, and the 103rd-floor Skydeck puts you high into the heavens. Take the ear-popping, 70-second elevator ride to the top, then step onto one of the glass-floored ledges jutting out in mid-air for a knee-buckling perspective straight down. On clear days the view sweeps over four states. The entrance is on Jackson Blvd. Queues can be up to an hour on busy days (peak times are in summer, between 11am and 4pm Friday through Sunday).
A bit of history: it was the Sears Tower until insurance broker Willis Group Holdings bought the naming rights in 2009.