My favorite highlight was the view on top of the Sears Tower. Especially the sunset! From my point, that really is a must-do.
The entrance fee was USD per person. First you see a little movie about the history of the Tower and then after that you go directly to the top.
Quick Tips:
Another great place in Chicago is the Hancock Center. A little tip from me is, don't go to the observation platform, go to the bar inside the tower. The bar is just one lever below the platform and you don't have to pay a fee. You get the same great view and a drink on top of it for the same amount you would have to pay for the entrance.
Another tip from me is to see the Buckingham Fountain in the Grant Park, especially at night with the changing light and the music; and after that you can do a walk on the coastline to the Navy Pier.Best Way To Get Around:
The best way to get around is with the public transport. I got a three-day pass for and I could use ALL the buses and the CTA trains as much as I wanted. They offer different days for the pass.