Big South Fork National Recreation Area encompasses 195 square miles atop the Cumberland Plateau where the upper reaches of the Cumberland River tumble over high bluffs, carving deep gorges and sandstone arches. Tennessee Landforms counts over 100 arches of varying size, and a dozen rock chimneys. The Twin Arches formation is one of the largest in the Eastern US.
Big South Fork offers a dizzying array of trails and dark canyons to explore -- more than enough to spend weeks exploring without doubling back. The park's website has a brief overview of some of the more popular trails here: Tennessee Trails, Kentucky Trails. They provide some crude, hand-drawn maps for some of these routes. The most comprehensive trail map is posted here. And here's an overview map. National Geographic's Trails Illustrated Map #41 covers the area.