Luray Caverns, http://luraycaverns.com/ August 10, 1977.
My family had traveled down to Falls Church Virginia to see my Aunt Marie & Uncle Andy - the same uncle who first introduced me to Miniature wargaming, stamps and coins. After spending a couple days at the Smithsonian, my Uncle took us to Luray Caverns and there I was introduced to a wonder. The cavern is impressive, all the moreso when you account for the ghost stalactite that one can see from 7 or so different places during the tour, and just how cool (literally and figurately) the place is. The bombshell for me however is the stalacpipe organ in the main cavern, operated by a custom console that produces the tapping of ancient stalactites of varying sizes with solenoid-actuated rubber mallets in order to produce tones.
As we listened to this amazing instrument, my mind instantly started working on the next level of The Castle of the Bloated One. We purchased one of the original 33 albums (vinyl, ah how I pine for thee) and I used it, along with the images I'd taken on the trip to lay out Organ Donor.