There is an unpredictable and beautiful-sounding Sea Organ, or Morske Orgulje, located on the edge of the Adriatic Sea in Zadar, Croatia. The 35 pipe ocean current instrument was built along the city’s promenade in 2005 by architect Nikola Bašić. From PublicSpace.org:
A series of polyethylene tubes of different diameters run along the inside surface of each flight of steps, connecting the submerged part with a gallery that runs along beneath the parade. With the variable force of the waves, the water penetrates the lower end of the tubes and is carried into the subterranean gallery, which collects it and returns it to the sea. In this process the air of the interior of the conduits is pushed to orifices that connect the gallery with the surface of the parade, generating sound vibrations which, given the variations in the diameter and length of the tubes, cover a broad range of musical tones.
Related reading: The Wave Organ in San Francisco.