I have this around for simple scenario images at work (i.e. a battlfield terrian showing anti-aircraft threats on the ground with aircraft flying overhead and radiation jamming signals, comm signals, etc). But every once in a while I feel like trying to make something nice-looking. National Geographic had an article last year on a cave in Viet Nam, where the roof collapsed and all sorts of foliage grew on the rubble pile. Gorgeous image. So I took a whack at it, strictly from memory. I was actually think more "lave tube" than plain ol' cave.
Carved out some more space upstage, widened it from a tunnel to cave looking into a tunnel. Yeah, slow day at work.
