Similar to GtheG really - apart from the acoustics of various Pre-Historic Tombs (West Kennet) I've sang & played in with various primal harmonic flutes & animal horns.

I think the very oldest I've ever played were two lumps of rock on the beach near Marsden Grotto in South Shields which chimed a perfect minor-third with such perfect resonance it struck primal fear into my heart. Huge they were - and much too heavy to bring home or even cart up the cliff to the car park. Never found them again...

The oldest in my keeping are various stones with holes deep enough to play after the fashion of a syrinx. I like to think I wasn't the first to use them!