Mauritania
The Richat Structure in Mauritania, also known as the Eye of the Sahara, is a landmark for astronauts. If you’ve been busy doing experiments and haven’t looked out the window for a while, it’s hard to know where you are, especially if you’re over a vast 3,600,000-square-mile desert. This bull’s-eye orients you, instantly. Oddly, it appears not to be the scar of a meteorite but a deeply eroded dome, with a rainbow-inspired color scheme.