Nice work AC, though I would like to see it in higher resolution / larger size.

Part of the problem with 4-8 not looking underground is that the shadow from 3 extends over and into 4 and all those rooms should not have shadows on the outside of the walls which is supposedly underground. The wall shadows make it look like the walls are above the sand. I think it might also help if the sand were darker on the whole half of the map that is subterranean.