The Sea Organ (morske orgulje) is located on the shores of Zadar,
Croatia, and is the worldâ€™s first pipe organ that is played by the sea.
Simple and elegant steps, carved in white stone, were built on the
quayside. Underneath, there are 35 pipes with whistle openings on the
sidewalk. The movement of the sea pushes air through, and â€“ depending
on the size and velocity of the wave â€“ musical chords are played. The
waves create random harmonic sounds.
-- Odd Music.com
More information and an audio file at the link. Via Mirabilis