This is the front of the grotto, which was in a vacant shop. The front windows were boarded over, the main shop doors held open and a tunnel built. I then painted these boards and the tunnel. Most of the customers apporached the grotto from the right so I painted the trompe l'oeil stone work of the tunnel entrance to fit that perspective geometry (Which is why it looks strange in this photo)

Photo on the right taken looking down the tunnel to the boards at the end. The visitors turned right at that end board to enter the grotto.