The most visually beautiful aspects of the ancient chapel, and considered the best of their type in the world, are its stained glass and rose windows added to the upper chapel in the 15th century.
During the French Revolution, the chapel was converted to an administrative office, and the windows were obscured by enormous filing cabinets. The all-but-forgotten beauty was thereby inadvertently protected from the vandalism rampant at the time.
See also: Paris Hall of Justice