The Chicago Botanic Garden is beautiful to explore and has a lot of foliage and walking trails. This is also where Patrick proposed to Maria :)
If you're near downtown, the Art Institute is a great art museum to explore. It's next to The Bean, Millennium Park, and Maggie Daley Park too so you could visit those on your way.
If you're near downtown, another great option is booking tickets for the architecture boat tour. The boat tour takes you down the Chicago River and details the history and buildings in downtown Chicago.
If you're near downtown, another great option is booking a show at the Second City Comedy Club. They have a running list of a number of sketch comedy and improv shows.