This magnificent Royal Chapel was ordered by the French king Louis IX (also known as Saint Louis) to house holy relics he acquired, including the Crown of Thorns. The main highlight of the chapel is perhaps the abundance of stained-glass windows that take up much of the wall space--the majority depict biblical scenes, including the rose window displaying the Book of Revelation, while one the windows shows the story of Louis and the relics.

Some have called the building "a reliquary turned inside-out", which means that in this case, the most sumptuous decorations are to be found inside.