The eastern U.S. state of Tennessee is home to some world-famous music venues: the blues capital of Beale Street in the heart of Memphis, the Ryman Auditorium, often referred to as the Mother Church of Country Music, and the rolling hills of the Cumberland Plateau. Actually, it's under the rolling hills of the Cumberland Plateau that you'll find one of the world’s most unusual performance spaces, Bluegrass Underground. On most Saturdays, between 500 and 600 music fans from all over the world trek nearly a kilometer into the Cumberland Caverns, and 110 meters down, to enjoy this original American music form. The performances are staged in a large cavern referred to as The Volcano Room. The room’s acoustics are nearly perfect. That fact was not lost on Todd Mayo, the Tennessee music promoter who originated the Bluegrass Underground in 2008. “Inside the cave we took the tour and you get down into the Volcano Room and there is this giant chandelier. And I looked up and I looked around and I said to the tour guide, ‘Do you all have live music around here?’" he recalled, "and she said, ‘No, but that would be a good idea.’ And it just sort of all came to me.” 18th century music for 21st century audiences The shows in The Volcano Room feature artists playing so-called American Roots Music, developed by immigrants from the British Isles who settled in the hills above in the late 18th century. It is considered "roots" music because it served as the basis of music later developed in the United States, including rock and roll, contemporary folk music, rhythm and blues, and jazz. After entertaining more than 180,000 guests, Bluegrass Underground is gathering an international following. That recognition is due in no small measure to the worldwide distribution of performances by the U.S. public TV system, PBS. “We have had people from Ireland and Japan," Mayo says, "and they literally, they said they came to America, the impetus was to come to this cave and see this show.” On a recent Saturday, after performances by The Way Down Wanderers and Flatt Lonesome, bluegrass fan Gwynn Lanaus admitted he felt a bit queasy being so far underground, but also said the music seemed to fit the setting. “The Bluegrass we saw today, it kind of blended. It might not be a venue for all kinds of music, but it was certainly appropriate for the day.” And the cave setting also matched the nature-themed songs often performed by The Way Down Wanderers. Lead singer Austin Thompson was impressed as well with the cave’s natural acoustics. “I thought it was really great," he said. "I mean, being on both sides of the spectrum, being on stage and as a listener in the audience, it was a really full… a really full sound.” Todd Mayo says he hopes in the near future to give music fans who attend the show an even fuller experience. He wants to develop a weekend long Tennessee experience that would include visiting some of the state’s many scenic parks and forests.