On the trip north from Tennessee to Cincinnati, we visit the homes of two U.S. presidents, the birthplace of another, and a natural wonder that once drew visitors from far and wide. — [Editor’s Note: Over the course of 2022 and 2023, New American History Executive Director Ed Ayers is visiting places where significant history happened, and exploring what has happened to that history since. He is focusing on the decades between 1800 and 1860, filing dispatches about the stories being told at…