Though damaged during the French Revolution, the 36-m long, 17-m wide, and 42.5-metre high Holy Chapel was restored in the 19th Century. It is fronted by a two-storey porch with a single nave and a chevet with seven panels. The chapel’s slate roof is dominated by a 33-m high cedar spire.

The sculptors, painters and architects were careful to present the spacious upper chapel in plenty of light and color, combining the chapel’s harmony of art and religious faith. This part of the building was reserved for the king, his family and friends, as well as for displaying the religious relics. The vaulted ceilings of this upper chapel, painted to resemble stars, gloriously accent the stained glass windows, as the sculpted décor presents peaceful statues of the 12 apostles. The holy relics, including pieces mentioned in the bible, were kept in a large decorated reliquary at the open tribune. They were exhibited to worshippers each year on Good Friday.

The lower chapel is dedicated to the Virgin Mary – the statue stands next to the central pier of the portal, and was once reserved for the palace staff of the monarchy. Low vaulted ceilings rest on columns with crocketed capitals, yoked with wooden and stone braces. Surfaces are painted with blues, reds and greens with gold patterns, and the walls decorated with 12 medallions representing the 12 apostles. Curved stone steps lead to a room that is three-times higher than it is wide. The stained glass windows, which reach to the roof, portray bible stories, as red and blue light flood the room.

Saint Chapel is famous for its stained glass windows, comprising a total area of 600sq m. Two-thirds of the windows are original works, representing 12th-century craftsmanship with its reds and blues. The 15th-century western rose windows, with each window divided into arches, tells the biblical story of humanity from Creation to redemption through Christ, read left to right and top to bottom. This biblical history covers themes from the books of the Bible and apocrypha, namely Genesis, Exodus, Numbers, Deuteronomy, Judges, Isaiah, the Tree of Jesse, Saint John the Baptist, Daniel, Ezekiel, Jeremiah, Tobias, Judith and Job, Esther, the Book of Kings, as well as the history of the relics. One of these windows describes, in 67 panels, the history of the treasures of Sainte-Chapelle from 1237, when Baudouin II, the fifth Latin emperor of the Orient, decided to give up the relics of the Passion of Christ to Saint-Louis, for their entry into the repository prepared for them by the king, Saint Nicolas. Damaged during the French Revolution, Saint Chapel, with its stained glass windows, was restored in the 19th Century.