Completed in 1248, the royal chapel Sainte-Chapelle in Paris was the residence for the Kings of France until the 14th century. Designed in the era’s most ethereal gothic style—called Rayonnant—this towering monument possesses an astonishing 1,113 stained-glass windows, among the finest in the world. How does such a slim-lined and refined structure support all those windows? All is explained in this virtual tour, led in reverent tones by Dr. Steven Zucker and Dr. Beth Harris. —E.C.