Nice start. My first suggestion would be to select your inside, expand the selection about 10 px or so, and then invert the selection and make a channel. Create a new layer and fill it with noise and set the blend mode to overlay and add the channel to the layer as a mask. This will put some random clouds over your "rock" parts and give them much more variety in dark/light tones. Of course, this depends on where you are going with the whole thing.
As for the walls, if PS supports it(GIMP does), I would select the walls and create a path from this. Then, unselect and stroke the path with a suitable texture you like(on a separate transparent layer.) I would probably also do the same noise thing on the floors layer to get some variation on the floor color also.
Hmm... how come some of the floor has a slight bluish tint???