I spent quite a bit of time exploring Chicago back in the very early 90's on an extended business trip. In addition to the museums mentioned already, there is also the Museum of Science and Industry. Interesting, but the exhibits were rather old and tired and the information outdated. Hopefully, its improved, if its still around. Also, Shedd Aquarium was pretty neat. I thought the Lincoln Park Zoo was a let down. The animals mostly seemed to live in concrete block, barren cages as I remember. Not a natural looking environment at all. Perhaps its been updated since then, though. I do remember the gorilla exhibit where there was one gorilla who absolutely hated one particular zookeeper. His hair would stand erect and he'd start throwing things and making a big commotion every time this particular zookeeper showed. No one could explain why.