Tunnel Passageway

You descend down main tunnel in a steady descent. The tunnel eventually gets larger and larger until the ceiling is high enough that your lantern light barely touches it. The walls are rough but worn smooth in places, as if many things have passed through here over a very long time.

Then your lantern light catches a narrow side passage that breaks away from the the main tunnel. The side passage bends sharply after only a few steps, hiding whatever lies beyond in tight, airless darkness.