Seen some nice photos of caves with beams of lights coming down the ceilings, but it seems Terragen isn't the best solution for cave scenes so I just went improvising on and on.
It's a good idea and a good start. Maybe break up the sunlight a bit so not all the details of the pit are washed out?
I like the concept, and a good start. Your scene is inspiring me to have a go at something similar.
You could try building up the walls and most of the ceiling from a bunch of cubes, give them all the same displacement and texture.