This is one of a handful of subway entrances designed by Hector Guimard, a master of the Art Nouveau movement. Most of the entrances he designed are gone now, and so was this one—originally constructed around 1900—until it was completely rebuilt as an identical copy in 2000.
This entrance is on the pedestrian Place Sainte-Opportune, and leads into the cavernous Châtelet-Les Halles Métro station.
The nickname for this entrance, Libellule, means “Dragonfly.”