The tunnels were drilled about 100 years ago to tap the ground water that slowly worked it's way down through a thousand feet of rock. Pretty much it's all gone in this tunnel, but at this dike moisture is present, and the ground although covered now in dirt, is dam and some times muddy.
As the saying goes, "there is light at the end of the tunnel". The bright shinny stuff on the roof of the tunnel are tiny water drops. I guess water still seeps down from above.
