Mentioned by Leisure Pass Group
10+ Free Things to Do in Chicago & How to Save on the Ticketed Attractions
"Nestled in Lincoln Park, this 35-acre zoo is an urban refuge for creatures from around the world. Admission is free (although you do have to pay if you want to ride the train or the endangered species carousel), so you can explore the many animal exhibits to your heart’s content. The Lincoln Park Zoo is home to over 1,100 animals, representing around 200 distinct species."