The white seems very flat, though I like the impression it gives some small amount of shading may look a tad better.
You could also try to reveal a touch more detail in the top right of the image especially if your sticking with the solid white, it detracts from the picture with the sheer lack of details. Nothing prominent but just subtle I feel could work better.
What I’ve actually got outside is a simple subdivided plane with a displacement map added to it… (simple and it kinda works :P)
And I really don’t know myself what I want the world outside the cave to be, most of the time I’ve thought of it as a jungle but to be honest I’m not very professional and I can’t make a entire forest in 3d outside that cave. Dinos would work but the same thing there, I can’t make a entire dinosaur, and would a siluette be enough to add something to the picture?
Towers should be easy to add but that would lead away from the feeling I’m trying to get…
I could try to place a simple image of a forest outside or maybe add some more (closer) mountains in the background and reveal them. I’ll have to try some diffrent things and see if it turn out good.
Yea, I’ll try to add something far back in the picture, something like a pack of longneck-vegetarian-dinosaurs in the distance. Maybe I also can add some low detailed flying dinos which could be a little closer, without erasing all the possibilities of the viewer to imagine though.
I’ll have to step back to modelling stage and see what I can come up with.