In the biggest park in Chicago, Lincoln Park (1,200 acres) you can find peace to spend there your entire day. One of my favorite spots is Lincoln Park Zoo, after almost 8 years of living in Chicago, I finally got a chance to do my trip there. And I gotta say I wasted 8 years! This place is amazing, and highly recommended for everyone living in Chicago or visiting!
I think the photos will speak for themselves, the admission is free and the park is open all year round, but remember to make a reservation if you want to visit the conservatory.