Eye of Africa, Mauritania

The Eye of Africa — whose official name, the Richat Structure, seems so mundane in comparison — was spotted in central Mauritania by astronauts on early space missions. In the expanse of the Western Sahara Desert, the formation has a diameter of about 48 kilometres. At first, scientists thought a meteorite had hit the Earth, causing this impression. But now it is believed to be a symmetrical uplift that erosion has revealed. No one has explained yet why it is circular.