Here you can see things coming together. One pic features the assembled concrete sleeve section of the tunnel assembled, turned with the blasted out portion visible. This side will be facing the wall away from the viewer on assembly. You can also see my experimentation with spackling (extremely useful and versatile stuff). I would slather some on, let it partially dry, chip away at it. I also used some WS rock castings and integrated them into the model also. I painted the whole thing flat acrylic white (I find that works better than just applying the colors directly to the spackling). You can also see the viewing portal as the rest of the mountain around the third tunnel is reassembled.