The Barabar caves in India are cut out of solid stone with mathematical precision.
https://void.cat/d/7s77wqZdVtPVVDLnurJCpy.webp
The surface has been polished to the degree that the smoothness exceeds the perception of the human eye.
How did they do it? We dont know.
Why did they do it? We dont know.
But this is an acoustic resonance chamber built by Les Paul...
