An underground chamber large enough to create echoes. Tennessee’s Camps Gulf Cave, a ﬁve-mile system, for example, contains what may well be the largest underground chambers in the Southeast, including its third room, known as Echo Hall. An echo hall can also be an acoustically resonant grotto, natural amphitheater, or side canyon. Saxophonist and composer Paul Winter explored the Grand Canyon in search of a “great acoustic place” that would capture the majesty of the canyon. After several quests, he found his dream “sound-space,” a sanctuary enfolded by an eight-hundred-foot wall of Navajo Sandstone. Winter named this place Bach’s Canyon, and he writes that within it “the sound was sublime, with the same seven-second reverberation time as in the Cathedral of Saint John the Divine in New York.” Bach’s Canyon is the setting for two of Winter’s recordings, Canyon and Canyon’s Lullaby.