You race back outside and grab your pack, but the contents spill out. Hastily, you scoop everything back into the pack, but it takes several moments. By the time you get back into the cave, the sound is gone. You pause for a minute, straining to hear anything, but all you can make out is what sounds like gurgling from a stream somewhere nearby.
With a shrug of the shoulders and a deep breath, you conclude that you were hearing things. But, just to be safe, you strap on your headlamp and flick it on. The cave is bathed in the pale white light that the small LED's push out. The stone walls are featureless, save for some moss that seems to be growing. You grab your journal from your pack and make notes of the cave walls, it's relative dimensions, but there's not much to see so far. The tunnel is fairly straight, with a gentle downslope. If water made this, it was for water to flow into the passage, not out. This fact puzzles you as the nearest stream is just over a mile away, and you aren't sure seasonal flooding would be responsible for a tunnel this big. As you proceed down the tunnel, your lamp catches a reflection from a narrow side passage that you would have otherwise missed. As you stop to look more closely, you can hear a trickle of water coming from the passage.