were shaped by running water. After twenty feet or so, the tunnel curves. You wonder where it leads. You venture in a bit further, but you feel nervous being alone in such a strange place. You turn and hurry out.

A thunderstorm may be coming, judging by how dark it looks outside. Suddenly you realize the sun has long since set, and the landscape is lit only by the pale light of the full moon. You must have fallen asleep and woken up hours later. But then you remember something even more strange. Just last evening, the moon was only a slim crescent in the sky.

You wonder how long you've been in the cave. You are not hungry. You don't feel you have been sleeping. You wonder whether to try to walk back home by moonlight or whether to wait for dawn, rather than risk losing your footing on the steep and rocky trail.