I sure wouldn't have known any better when I was an AOW student, but kudos to those who do. I have to believe OW divers are quite safe in the upper cavern just beneath the overhang, but my Fundies instructor's point that that sloping overhang was the dividing line between open water and something else stuck with me. "Almost open water" is not open water. There's often no real dividing line once you get into a cavern--it just gets deeper and darker. And now as a Cave 1 diver I'm totally anal about my primary tie-off not being under any overhangs. But I digress. Not relevant to Blue Grotto.I’ve heard of instructors trying to take AOW students into the lower cavern and the students refusing.