Kings like to have a bit of privacy when they go to Church. This was no different with Louis IX of France. Next to the grand Notre Dame in Paris, which was destroyed in a fire in 2019 and is now being restored, stands a small chapel. It is much smaller, but probably they used more gold and fabrics when they created it.
A large part of the Sainte-Chapelle was destroyed during the French Revolution, but restorations in the 19th and 21st centuries made it a beautiful place to visit today. Especially the stained-glass windows are a feast for the eye.