Bibliothèque nationale de France (Richelieu)

Henri Labrouste's Salle Labrouste at the Bibliothèque nationale de France in Paris (1868) is one of the architectural wonders of the 19th century: nine cast-iron domes supported by slender iron columns, each dome pierced with an oculus flooding the reading room with diffused natural light. Restored magnificently and reopened in 2022, it is arguably the finest reading room in the world.