I visited Hopewell Culture National Historical Park - Mound City (early evening) and Newark Earthworks - Great Circle (just after sunrise). Besides what I explored, Seip Earthworks is considered and often recommended as the other key remnant of "Hopewell Culture". The other components, while important archaeological sites are perhaps more for completists.

As Mound City is managed by the National Park Service the interpretation is quite good and as I arrived just before a major storm, I had a personal guide for a full hour before the downpour began. We began at the short nature trail, highlighting the native plants, including what would and would not have been present a millenia ago. As you approach the Scioto River, there are interpretive panels worth reading. An exceptional fact of "Hopewell" is that in Ancient North America, the rivers were the "highways" of their time. Scioto River connects to the Ohio River, the Ohio River connects to the Mississippi River, the Mississippi River connects to the Missouri River, and the Missouri River connects to Yellowstone River. There is a place called "Obsidian Cliff" in Yellowstone National Park (a National Historic Landmark), which includes panels about its importance to indigenous people (most visitors drive right by which is understandable). Obsidian from this cliff in Yellowstone has been found in archeological digs at Hopewell. The "Great Circle" at Newark is impressive, yet doesn't have the same amount of interpretation as the National Historic Park, which these sites really benefit from. Arriving just after sunrise added to the atmosphere, yet from the ground, the scale of these circle mounds are difficult to fully appreciate. 

For logistical reasons Columbus, Ohio is the best place to access these earthworks. Hopewell National Historic Park (Mound City & Visitor Center) is about 50 minutes drive South from Columbus and Newark Earthworks are about 40 minutes drive East. Seip Earthworks would require another 20 minutes of driving past the Hopewell Culture Visitor Center.