The western side of the island has a gigantic cave with a grassy floor, that was probably carved by the sea when the sea levels were much higher, thousands of years ago. The cavern is 130 meters wide, 60 meters high and 60 meters deep. From a certain angle, the island looks like a skull — hence the name Skull Rock — complete with a big cranium, an eye socket (the cave) and the bridge of a nose. The cave was once thought to be used as target practice by passing ships.
There are actually two large caves on the western side. The roof of the smaller cave is some 25 meters above the sea and forms the floor of the upper larger cave, and is covered with soil and vegetation on its surface.
The island is practically inaccessible with tall vertical cliffs and no place where a small boat could come ashore and anchor. Because of this, few people have set foot on the island or explored the cave. Those who have reportedly discovered cannonballs inside the cave.
Birds, particularly the Black-faced Cormorant, have taken advantage of Cleft Island’s isolation and inaccessibility to humans, by making the island it's home.
According to amusingplanet.com