Paris, French National Library / Bibliotèque Nationale de France, Site Richelieu (salle ovale)

Labrouste took an even bolder approach in his design for the national library on the Rue de Richelieu, opened in 1868. A stony fortress from the street, the library warms up once you step inside. The reading room is punctuated by nine terra-cotta domes, each open to the sky at the top. The Salle Ovale with its glass ceiling is another heavenly space for scholars.