Off the southwest corner of Mauritius, in the Indian Ocean, is a rather extraordinary phenomenon: what appears to be an underwater waterfall. The photograph and Google satellite image below show what looks like a cascade of water pouring from the shallows around the island into the abyss below. But it is, in fact, an illusion. The effect is caused by silt eroding at the edge of a very steep coastal shelf, as explained rather beautifully on this page here.
The fact that it is not a waterfall, however, does not make it any less spectacular.