What do to while visiting Chicago?

Travel Info
I'm going to a concert in Chicago, and also a Cubs game. I think we'll probably go see the Sears Tower too. But other than that I've never been to Chicago so I don't know what there is to do. What are some things to see that won't take all day (we'll probably have like 5-6 hours of free time) and are also close to a transit station, because I won't have a car?

Travel Tips

Free Stuff: Navy Pier, The Miracle Mile (window shopping and people watching is always worthwhile), The Art Institute (free day is Tuesday), Grant Park and Buckingham Fountain.

If you're up in Wrigleyville, walk across to the Cubby Bear Lounge and have a beer...it's a tradition.

The "el" trains (for "elevated") go everywhere for about a buck and a quarter. The State of Illinois Building is their terminus in the Loop and worth seeing as it has the largest and perhaps least efficient "green" air conditioning system in the world. Walk around the Loop (called so because the "el" tracks loop around to go back along their routes). Enjoy the interesting architecture and public art. The Art Institute lions may be wearing their Cub hats...they are an institution all by themselves.

Make sure you eat something! Chicago is a food town and invented deep dish pizza. Pizzeria Uno or Gino's are the spots to go. Or perhaps the Billygoat Tavern for cheeseburger! cheeseburger! cheeseburger!

Enjoy!
Others

Go to Navy Pier. There is a lot to do and see there. Go up in the ferris wheel, take a boat ride, shop. It's fun.
Check into a hotel and hide.
not too long ago a friend told me if you plan a trip to chicago on the right days there are a ton of free museum and art exhibitions... maybe you could look into that.
Millennium Park
Magnificent Mile
Go to Navy Pier, shop on the Magnificient Mile, go to the museums and aquarium. You don't need a car, you can walk or take a taxi.
From the cubs game take the "EL" (elevated train) downtown. take a boat ride on the chicago river AND lake michigan to get a cool perspective of the city at the right speed. Take a walk down michigan ave and enjoy the magnificant mile from the wrigley building. Head over to Uno's for a memorable chicago pizza. Take a taxi and ask the driver to take you under the city on lower Wacker and finish at the field museum or the planetarium and enjoy the sights and walk through grant park, If you can rent a bike take a long ride along the lake and stroll through the Zoo. If you have time and the day is clear head to the sears tower. Alternate lunch spot is greek town --those are my favorite spots when I go back and I've lived there 1/2 my life. Go rent the Blues Brotthers & Ferris Bueller's Days Off movies before you go Happy Trails

p.s you'll need a few days rather than a few hours to appreciate Chiago