The Grotto, Sinkhole formation in Port Campbell, Australia.

The Grotto is a sinkhole and arch-like opening in the rock on the Great Ocean Road outside Port Campbell, Victoria. It was formed by erosion: wave action and salt crystals prising apart horizontally bedded rock. Wooden steps wind down the cliff face to a viewing platform, and at low tide you can enter the cave and see the pool behind it, which does not empty at low tide.

The Grotto formed through erosion: wave action and the salt in seawater worked into cracks and pores of the rock. During low tide the water evaporated and salt crystals pressed on the stone, loosening it. Its name comes from the arch shape that recalls a grotto, and the horizontal rock layers make it look almost man-made.

The name comes from the arch shape that recalls a grotto, and the horizontal rock layers make it look almost man-made. Visitors reach a viewing platform by wooden stairs; at low tide they can step inside the hollow, which is otherwise washed by the sea.

Access is via steps from the main parking area, and it is best visited between sunrise and sunset. At low tide the natural rock formation becomes particularly visible and offers a better view of the pool below.

During low tide the formation creates a sheltered pool that remains filled while the surrounding basin appears dry. This contrast between water and exposed rock is a fleeting feature that changes with each tidal cycle.