When I first saw this organ on a small stage deep inside Luray Caverns in Virginia near the Shenandoah National Park, I thought “big deal, it is just an organ”. But no….they had an electronic organ, but it didn’t play internal pipes, but actually played hundreds of stalactites on the roof of this cavernous hall. They found that by gently hitting some stalactites with a hammer, they produced a beautiful sound. So they set up hundreds of electronic actuators (hammers) all over and tuned them and attached them to the organ. They played lovely music live on the stalactites! A stalactite organ. The lower photo shows a few actuators.