Have you ever turned your computer's sound program to the visual setting, and just stared at the designs for while being mesmerized? This is like that, except using real earthly elements.

Nigel Stanford, a New Zealand musician, uses water, fire, sand, and other elements to make his music visible. According to this story on NPR.org:

Cymatics is the science of visualizing sound. What New Zealand musician Stanford does in his cymatic experiments, however, is itself an art form. Using a variety of methods, he and his team make the complex spatial patterns generated by his own music visible — and it's a feast for all the senses.

While cymatics is something way over my head, the effect is not - beautiful designs and reactions in the elements caused by sound waves. Many performers have used cymatics in their shows (Blue Man Group, etc.), but this video is the best manipulation of sound waves I've personally seen.