Clingmans Dome is one of the most popular destinations in the Smokies, but few people truly know what lays below! Underneath Clingmans Dome Road, an ornately decorated hidden tunnel stands alone. It’s most commonly referred to as the Thomas Divide Tunnel, but it’s also frequently called the Thomas Ridge Tunnel, the Old Mule Tunnel, or other variations. Although it was once located on a hiking trail, the secret tunnel under Clingmans Dome is now one of the park’s best hidden treasures. Here's everything you need to know about the hidden tunnel beneath Clingmans Dome: