On the island of Mauritius, a naturally occuring optical illusion can be found, via these aerial Google Earth photographs, on island's Southwestern tip. From these photographs, found via Exposure Guide, it looks as though the ocean itself drops like a waterfall. The illusion is caused by the sand, which maeks up the light part of the water. The current makes the sand disperse in a waterfall pattern, as though an underground waterfall is tucked just off the island's coastline.
via Exposure Guide