Best Free Midwest Attractions: Illinois

Cahokia Mounds State Historic Site, Collinsville About 15 miles east of St. Louis, you can see 100-foot-tall Monks Mound (left), the largest of the area's 80 surviving ceremonial mounds from the time of the Mississippians. An interpretive center includes a re-created village and orientation theater to help visitors visualize the city that sprawled here centuries ago.

National Great Rivers Museum, Alton Steer through locks on an indoor barge simulator, one of 20 interactive exhibits that teach visitors about the Mississippi and other rivers. The museum is about 30 miles north of St. Louis and just across the Illinois border.

Cahokia Mounds State Historic Site

National Great Rivers Museum