The Great Serpent Mound
Adams County, Ohio
This 1,348 ft feature was built by an ancient culture (researchers are still debating which, though carbon dating has more recently suggested the Fort Ancient Culture in about 1070 ce) in the foothills of the Appalachian Mountains. Despite original beliefs that it was used as a burial mound, it is unclear exactly what the purpose was of building this giant effigy. It is placed on a plateau next to a crater, now currently part of a state park protected by the Ohio Historical Society and the Arc of Appalachia Preserves system. Park entrance is free with an $8 parking fee. Summer bucket list, anybody?