You shine your flashlight down the tunnel. You can make out rough shapes along the ceiling and realize it's a flock of bats sleeping. You move the beam downward and see the tiny shapes of rats and insects scurrying along in the distance. Great clumps of green moss and grasslike plants line the river of sludge along the bottom. The liquid is dark and opaque; the flashlight does not penetrate its surface. You can follow the walkway to your left, follow it downwards to your right, or you can give your whistle a try.