The Gap Cave Trail at the Cumberland Gap National Historical Park in Virginia, near Cumberland Gap, is a short 0.2 mile out-and-back hike from the Wilderness Road Trail to the Gap Cave and back.
Gap Cave is formerly known as Cudjo's Cave and lies right on the Virginia and Tennessee border and lies just below the Pinnacle Overlook Trail.
You can pay for tours through the cave and people are still discovering new section of the cave all the time. As of 2015, 18.5 miles has been mapped of the cave.
In order to reach the cave, take the Wilderness Road Trail west until you find signs for Gap Cave.