The "real" Sainte-Chapelle isn't on the ground floor, but is the wonder that awaits you on the upper floor, which was once reserved for the royal court and a few other privileged persons.
The architect Pierre de Montreuil, who is believed to have almost certainly designed the chapel, had the ingenious idea of inserting metal reinforcements into the masonry walls that made it possible for them to be thinner and very much like a slim and elegant frame around the multicolored windows. Thus the building loses its consistency, and looks like pure architecture of light: transparent and immaterial.
But now you should immerse yourself in the over 1100 window panes that decorate the interior space with thousands of fairy-tale colors. The themes of the windows are the episodes of the Old Testament and are mostly focused on the kings of ancient Israel, thereby prefiguring and religiously legitimizing the sacred throne of the French monarchy. The statues of the kings of the Bible that are in the Cathedral of Notre-Dame also follow the same logic. In the first window on the right you can follow the history of the relics that are conserved in the chapel.
The light also comes in from the large rosette, or the circular window on the façade, whose fifteenth-century windows depict the Apocalypse.
During the French Revolution the chapel was devastated and its relics were lost. Unfortunately, you also have to bear in mind that the necessary nineteenth-century restorations partly altered the chapel's original appearance. For example, only six of the Apostle statues on the pillars are from the fifteenth century, and the other six are from the 1800s. The two deep niches you see at the sides of the altar were the platforms reserved for the royal family. The baldachin that once contained the relics of the Holy Land is a copy of the original that was destroyed in the Revolution. Approximately 60% of Sainte-Chapelle's stained glass windows date back to the 1200s; the remaining parts have been added or replaced over time in various restorations, but at least the overall effect for this aspect is absolutely harmonious and integral.
FUN FACT: as you can imagine, Sainte-Chapelle was in a pitiful state after the Revolution. Fortunately in 1831, Victor Hugo published Notre-Dame de Paris, or The Hunchback of Notre Dame, and its resounding success brought medieval style back into fashion and hastened its restoration. In short, the novel saved the monument!
