Really, you know you are getting close when you see this! You could tell natural light was filtering in when the rocks started to be coated in an algae like growth. It was pretty amazing to see the moisture condensing in the top of the caverns, and it made it damp enough at the top of the natural entrance for this kind of plant life.
Looking good - nobody was too red in the face, though we were all a little wary of getting pooped on by the birds diving through the mouth area.
The eye of light is the natural opening, where the mud swallows that have nested on the walls dive in and out by day, and where the bats escape into the night at dusk. We didn't go back to see the bats as planned because we were all tired and hungry.