Stone State Park sits on the northwestern edge of Sioux City, where Iowa's Loess Hills begin to show themselves in wooded ravines and high ground above the Big Sioux River. It is the best nearby place to understand that this corner of Iowa is not flat cornfield country.
Trails, overlooks, and picnic areas make it an easy outdoor half-day. It pairs well with the riverfront history sites if you want Sioux City's landscape as well as its Lewis and Clark story.