When you are visiting Chicago, you have to take a ride to the top of the tallest building in the US (soon to move to third place, I believe). It used to be the Sears Tower but an insurance company obtained the building's naming rights and since 2009, it has been called the Willis Tower. The company has taken full advantage of the view there and its popularity with tourists, as you can see in this video!!
Anyway, it's really a great view from the 103rd floor of this 110 story building. On a clear day, you can see 50 miles in each direction and four states! And you are welcome to climb the 2232 steps to the top. The record time for someone to climb all those stairs is 13 minutes. I decided to save that for another day!