Pictures do not do this place justice and words cannot describe it.
From Wikipedia:
Begun some time after 1238 and consecrated on 26 April 1248,[2] the Sainte-Chapelle is considered among the highest achievements of the Rayonnant period of Gothic architecture. It was commissioned by King Louis IX of France to house his collection of Passion relics, including Christ’s Crown of Thorns—one of the most important relics in medieval Christendom.
Along with the Conciergerie, the Sainte-Chapelle is one of the earliest surviving buildings of the Capetian royal palace on the Île de la Cité. Although damaged during the French Revolution, and restored in the 19th century, it has one of the most extensive 13th-century stained glass collections anywhere in the world.