Bo Nau grotto which is about 200m wide, form the shape of a frog's mouth. The bottom is wide, flat and shadow, with stalagmites and stalactites jutting from above and below. At the entrance, three stones look like three monks with their heads close together. Two of them appear to be playing chess, with the third man serving as a referee. Bo Nau grotto faces the south and thus receives a very fresh wind as the waves crash against the cliffs.