|Called the Guelb er Richat, or the Richat Structure|
It's an elliptical dome in the western Sahara Desert, also called the Eye of the Sahara. What a fantastic name (occurs to me that it is straight out of H.P. Lovecraft). It's about 40 km in diameter - and apparently, not an impact crater. Geologists believe that it's a magmatic extrusion.
I was just goofing around, half-working on the Sahara desert south of Morocco when I should actually be working on my book. Ah, well, artists need to rest once in awhile.