Right at the border between North Carolina and South Carolina on Highway 281 is Upper Whitewater Falls, part of a cluster of falls on the Whitewater River which travels the intersection of North Carolina, South Carolina and Georgia.
Though there is some argument as to whether or not Upper Whitewater Falls is the tallest waterfall in the country -- or even the state, given the definition of "waterfall" -- but there's no denying that it's an absolutely spectacular site to behold. Housed in the Nantahalia National Forest, visitors can view the falls from a series of observation decks down a set of wooden stairs maintained by the National Forest Service. Direct access to the falls is impossible, and going "off trail" isn't encouraged in any way whatsoever, but the view from the decks is stunning. A $2 per car fee is the only cost of admission to this stunning sight/site.
For more on Upper Whitewater Falls: Interactive Map on Land of Waterfalls