I'm fine with what to do outside the tunnel entrance, but what do I do inside the tunnel entrance? What have others done for realism? How far have you ballasted up the tunnel? Do you put an arch (matching the portal) inside the tunnel? Maybe paint it black or something? Line it with brick paper et al? How far down the tunnel do you go? It would probably be fine if my hills were completely sealed at the back, however too much light is coming OUT of the tunnel and you can see all the guts and insides of my mountain! What have others done in this situation?