The area south of Columbus was a center for the ancient Hopewell people, who left behind huge geometric earthworks and burial mounds from around 200 BC to AD 500. This national park tells their story. The visitor center (8:30am to 5pm) provides intriguing background information, but the highlight is wandering about the variously shaped ceremonial mounds spread over 13-acre Mound City, a mysterious town of the dead. It's 3 miles north of Chillicothe, next to one of Ohio's largest prisons.
The park has other parts sprinkled around the area, including Hopewell Mound Group, the largest site, located a few miles west of Chillicothe; and Seip Earthworks, which holds some mighty embankments 17 miles west of Chillicothe. These farther-flung bits are less developed than Mound City, and you'll likely have them all to yourself.