Designed by I.M. Pei in 1989 using 666 glass panes (according to popular lore) built to Golden Ratio proportions ($\Phi$). In the subterranean Carousel du Louvre sits the Inverted Pyramid (La Pyramide Inversée), whose downward-pointing glass apex hovers just millimeters above a small stone pyramid rising from the floor (As Above, So Below).
The full decipherment and its observational protocol — where to stand, when, and what to watch for — are in the Paris field codex.
Or read the complete Florence codex free first.