Within the Luray Caverns in Virginia, United States, is an electric organ made of stalactites. It literally makes rock music.
Lithophones are some of the oldest instruments in the world. Certain types of rock, when struck, produce a ringing sound – a sort of stone xylophone. This phenomenon is of particular interest to acoustic archaeologists; we have evidence of bone flutes going back many millennia, but musical rocks are probably much older. The fourth link below has a nice demonstration of prehistoric music using lithophones.
Since the late 19th century, the impressive stalactites and stalagmites of Luray Caverns have been a popular tourist attraction. The whole cave system, in the Shenandoah Valley portion of Virginia, is frankly gorgeous:
But its most famous feature is a human / nature collaboration, the Great Stalacpipe Organ. The stalactites within the cave are lithophones. When struck (with a hammer or rubber mallet) they ring out loud and clear. And, in the 1950s, a chap named Leland Sprinkle found a stalactite corresponding to each note in the Western scale.
(Well, actually he either found perfect matches or shaved stalactites down until they produced the correct tones. Hey, it was the ’50s, a little destruction of natural wonders in pursuit of a quixotic dream was okay then.)
Once he identified all the right stalactites, Sprinkle attached a little device to the side of each one, a rubber mallet to trigger the tone. And he wired all those mallets up to a pipe organ console. Voila: stalactite music. You can literally play the rocks.
The stalactites are spread across a wide area (fourteen thousand square metres) but the stalactite music echoes throughout its whole expanse. This is what it sounds like: