We had the first of our certification dives today at the Hudson Grotto. This is a 130 foot sinkhole filled with low visibility tannin water. You had to go out to the barrels and defend to a platform at 20feet deep. E got scared but I enjoyed looking at the turtles and fish so I was good.Â Mom, Dad and I all did our dives. E will have to do a make-up dive since he refused to go under in the tannin waters.