When astronauts first saw the Richat Structure from orbit, they used it as a landmark to know where they were over Africa - it is that easy to spot. The rings are made of different types of rock that wore away at different speeds over millions of years, leaving ridges that look like the rings of a bulls-eye target.
The rocks in the outer rings are over 500 million years old. That is so long ago that even the dinosaurs had not appeared yet. Some of the rocks contain tiny fossils of ancient sea creatures, which tells us that long, long ago this part of the Sahara was covered by a shallow ocean.
For most of history, people on the ground could not really see what it looked like because you need to be very high up to see the whole pattern. It was only when aircraft and then spacecraft began flying over it that humans realised how incredible it was. Now scientists visit in jeeps to study the different rock layers.
Today the Eye of the Sahara is one of Mauritania's most famous landmarks. No one lives right inside it, but Tuareg nomads have crossed its sands for centuries, using its rocky ridges as shelter from desert winds.