The Eye of the Sahara is a bullseye of rock rings forty kilometres across in the Adrar region of Mauritania, and from where you stand on it, it looks like ordinary desert. There is no road to it. The drive from the old caravan town of Ouadane is hours of sand, wadi gravel and broken rock, with the driver reading the ground instead of a track, and every low rise you grind over is another ring. Guides carry the satellite picture and point out which one your camp is standing on. The single clue at ground level costs a few minutes of loose, clinking quartzite up to a crest. From there you follow the ridge with your eye: it runs straight for a while, then leans, and keeps leaning, until haze takes both ends of it.
No meteorite made this. The impact theory rested on grains of coesite, a mineral that forms only under the shock of a hypervelocity strike, and when they were re-examined in 1969 they turned out to be ordinary barite. What the rock does hold is old volcanic plumbing: dikes around a shattered core some thirty kilometres wide, dated to roughly a hundred million years ago. The rings are the worn-down roots of a dome, not the wreckage of a strike. Plato's Atlantis was rings of land with a plain beyond and mountains behind, which, read loosely, is why the internet keeps finding it here; nothing in the ground has ever agreed. Camp is inside the structure, where there is nothing to compete with the sky: no town, no road, no headlights on a horizon that is pure black. In the dry watercourses of that ring, worked quartzite lies loose among the natural rubble: more than two hundred Acheulean hand axes recorded, chipped from stone the rings themselves supplied. Your guide will show you how to tell a struck edge from a broken one, then ask you to put it back exactly where you found it.