A massive sinkhole and the deepest underwater cave in Australia. From a manhole sized hole in a paddock, there's an 8m freehanging drop to the water's surface. The cave is about 20m in diameter at this point, and the walls continue to widen out as you drop into the depths. Directly below the entrance hole is a feature known as the Rockpile. While this would originally have been a high point of the bottom in the natural formation of the sinkhole, the property owners later dropped a considerable amount of rocky substrate down the entrance. At the top of the Rockpile in about 36m of water, the cave is roughly oval shaped. At the two opposite ends, tunnels taper down into the depths. A swim out from the Rockpile brings you to Sawtooth Rock, a natural feature sticking up to 35m. From Sawtooth Rock you can look back towards the Rockpile and hopefully appreciate the shaft of light that gives this site its name.