Land Between the Lakes is pretty flipping cool. A decent actual off road park, and tons of sketchy pencil line roads.
This might disappoint the hard core off road types, but you can start at Land Between the Lakes, which has lots of camping opportunities, and spend a day or two green laning through the western tip of the Smoky Mountains to Chattanooga, which passes through a shed load of cool towns, (including Nashville) and another shed load of distilleries, including Jack Daniels'.
I have started exploring Middle Tennessee, and really love the place.