Chirped Echo from the Mayan Pyramid of Kukulkan at Chichen Itza: David Lubman of the Acoustical Society of America argues that the echo sounds like the primary call of the Mayan sacred bird, the Quetzal.
Moving Beyond Prophecies & Predictions: By Cynthia Gage (Atlantisrising)
Rock Art Acoustics: Steven. J. Waller's Home Page
Stone Structures and Sound: