Near the end of the tunnel it curves to the left. Because of that, as you climb the slope through the tunnel there's no light ahead of you until you get very near the end. When you come out of the tunnel there's another set of stairs on the right, and an opening on the left that takes you out to an overlook. Most people look to the right, express their opinion and go to the left. The square mark that you see on the wall ahead is a covered up opening into a room built in the far wall of the stairs.
Photo album created with Web Album Generator