If you're here during the winter skating is the best part of Millennium Park. It's free if you have your own skates or rentals are somewhere around $10 with no time limit. It's also a great place in the summer, there is Heaven's Gate (or the AT&T Bean), paths through the garden, fountain (with electronic images) you can walk through. The park vendors are very expensive so it's best to stop by Walgreen's across the street and get some snacks if you're planning on laying out in the grassy section of the Orchestra seatting.
6220 N Olcott AveChicago, IL 60631
9058 S California AveEvergreen Park, IL 60805