Up ahead, you can see that the tunnel is growing wider in all dimensions. Before long, you have room to stand and walk. The curve to the right ceases, and the tunnel begins to slope downwards.
The walls here are still made of the same plain, finished grey stone, but without the moss you can clearly see the impressive engineering feat that this hundred-metre corridor is.
Finally you see up ahead that the light is spilling out into a room of some kind, and you advance hurriedly towards it. There is no sound and no discernible smell around you, and therefore no clue as to what lies there.