Today on metafilter, I learned about The Great Stalacpipe Organ, the worlds largest musical instrument. It lives deep inside the Luray Caverns in Virginia's Shenandoah Valley. Througout the 3.5 acres of caves are rubber tipped mallets that tap the stalactites producing the required tone indicated by the 4 manual console. It was invented by Mr. LeIand W. Sprinkle, who was primarily a mathematician at the Pentagon. Truly amazing!