I have modified the walls to give them a little curved look (it is hard to see, but the resoult is a little better), and added mine carts (empty version yes).
I have also changed the ground texture to a stone one. Currently, I have two versions, but dont know which is better.
Also, should I change the ceiling to stone as well?
For me it looks ok, but I didn’t notice any difference in the background wall. Also you could put some stalactite and rocks on it. Are you already working in the gameplay part too?