The largest musical instrument in the world is underground in a Virginia cave

https://www.npr.org/2023/11/07/ [login to see] /the-largest-musical-instrument-in-the-world-is-underground-in-a-virginia-cave
In the rolling mountains of Northern Virginia, Luray Caverns are celebrating the 50th anniversary of their designation as a National Natural Landmark. They are the most extensive cave system in the eastern U.S., but for many of the million annual visitors, Luray Caverns are better known for their sounds. Luray Caverns are home to the largest musical instrument in the world.

A trek into the depths of Luray Caverns reveals a stunning spectacle; stalactite and stalagmites, golden rock formations, and crystalline limestone chambers carved out by water over millions of years. Pools of glassy, smooth water reflect the stalactites above. It creates the illusion of an underwater stone city. Tunnels wind throughout, leading visitors into a chamber known as The Cathedral. This is the heart of The Great Stalacpipe Organ.

It was designed in 1956 by Leland Sprinkle,

"Leland Sprinkle came through the caverns with his son on his fifth birthday. They would take a little rubber mallet and play a little song on the stalactites. And he got the idea of building an organ," said Larry Moyer, who started working at the Caverns for 42 years as a teenager and is now the lead engineer of the organ.