Big South Fork National Recreation Area encompasses 195 square miles atop the Cumberland Plateau where the beginnings of the Cumberland River tumble over high bluffs, cutting deep gorges and sandstone arches. If I don't have your mouth watering just yet, check out Tom Dunigan's indispensable Tennessee Landforms page to get an idea of just how much this park has to offer.
BSF offers a dizzying array of trails 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.