In the Sahara desert of Mauritania, this prominent circular feature has attracted attention since the earliest space missions. Why? Because in the otherwise rather featureless expanse of the desert, it forms a conspicuous bull’s-eye.
The site was initially interpreted as a meteorite impact structure because of its high degree of circularity, but according to NASA, it is now thought to be "merely a symmetrical uplift that has been laid bare by erosion."
Image courtesy of NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team