Congaree

What looks like a swamp is technically a floodplain: the Congaree and Wateree Rivers periodically overflow into this forest, depositing nutrient-rich sediment that has helped grow some of the tallest trees in the eastern United States. Loblolly pines and bald cypress here regularly exceed 130 feet, forming one of the highest natural forest canopies anywhere in the world, all inside the largest intact tract of old-growth bottomland hardwood forest left in North America.

A 2.4-mile elevated boardwalk loop lets visitors walk through the floodplain without ever touching the water below, past cypress knees, champion trees, and, if the water is up, a genuinely disorienting sense of a forest floor turned into a mirror. The park floods seasonally and unpredictably, and portions of the boardwalk occasionally close for repair or high water, so checking current conditions before a visit matters more here than at most parks.

Come for the scale of the old growth. Stay for the quiet, since this remains one of the least-visited and least-crowded national parks in the eastern half of the country. Read the story, check the live data above for boardwalk conditions, and when you leave, collect the stamp.