The side passage is very narrow. You remove your backpack, holding it by your side and turn sideways to squeeze through the narrow crack. You suck in the air and push your way through, feeling like wet laundry being forced through a ringer. With a heave you slip through and find yourself in a much smaller tunnel. You have to crouch to not hit your head, and the walls are much more coarser and, you realize as you think about it, much more natural. The main tunnel seemed too polished, and you wonder if it might have been made by a mining crew. No matter, it ended quickly, better to focus on the passage you are in.
Water is running through here. It's about 6 inches deep and your feet are already wet. The water is warm. Slipping your backpack back on, you splash some water on your face to clear the sweat from pushing you way through the crack. You take a moment to note the location on your journal, then scan along the two directions of the tunnel. It's dark in both directions.