Mammoth Cave National Park is a World Heritage Site and International Biosphere Reserve. It was designated a national park in 1926 and fully established and opened in 1941 -- 80 years ago. At 412 miles, the cave itself is nearly twice as long as any other known cave system. Geologists believe there may even be a couple more hundred miles of undiscovered passageways.  The Traveler's Lynn Riddick takes us to Mammoth Cave and taps into insight and anecdotes from park personnel about the historic and geologic wonders that tell the story of this unique geological and biological landscape.