Eventually the tunnel levels out and, rounding a bend, you begin to feel the air change. It is cooler here; wetter, and not as still. When the walls give way to a cavern you pause on the threshold and can sense the vastness of the space before you, though it is lost in the blackness beyond the circle of your torchlight. Despite the apparent impossibility, it feels like you are standing outside. So much so that a small doubt is planted in your mind. You can hear a cascade of water in the distance, and the air smells organic, like dirt and leaves. You look up, and see points of light that cannot be stars twinkling overhead. Curious, you douse your torch and wait for your eyes to adjust. More and more points of light become visible out of the dimness and here and there you spot some movement. Glow worms, probably. Casting your eyes back down, you gasp. Far from the inky blackness you expected here hundreds of feet below the surface, the cavern is filled with all manner of bioluminescence. You stand on a raised rock ledge – from there a dirt slope drops away perhaps twenty feet to where, revealed in the soft blue glow of mosses and fungi and things you couldn’t begin to identify, begins a vast forest.