From Odd Music: The Sea Organ.
The Sea Organ (morske orgulje) is located on the shores of Zadar, Croatia, and is the world’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 –- depending on the size and velocity of the wave — musical chords are played. The waves create random harmonic sounds. [continue, see photos, listen to sample sound]