D.K.
I like the other mom's idea about a walking trip, but here's a twist ... a lot of that stuff is around the Chicago area - what if you played tourist close to home? For instance, if you want to do something active, like canoeing on the Fox River near Ottawa, for that day you get a trusted sitter, if you go hiking at Starved Rock, put your precious little one in a framed backpack & have fun! Go see the whales at the Oceanarium at The Shedd Aquarium, or see Harry Potter at the Museum of Science and Industry, visit Sue the T-Rex at the Field Museum, take a skyline cruise, hit the beach at Oak Street Beach ... you get the idea. Play tourist close to home, get sitters for days that will be more difficult for your cherub and go play together. You'll have a lot of fun and save money - no lodging costs = more money for activities.
Have fun!
D.