Which cathedral's famous blue stained glass dates mainly from the 12th century?

Chartres Cathedral is famous for blue stained glass dating mainly from the 12th century.

The cathedral's windows are among the best-preserved large collections of medieval stained glass in Europe. Much of the surviving glass was installed during the rebuilding campaign after a fire in 1194, although some panels predate that event. The deep blue commonly associated with Chartres is especially prominent in the famous Notre-Dame de la Belle Verrière window.

The windows combine biblical scenes, saints, symbolic imagery, and representations of trades and donors. Medieval viewers encountered them as both religious teaching and luminous decoration. The glass was made from colored materials and painted details, then assembled with lead cames.

Chartres Cathedral is also celebrated for its French Gothic architecture, sculpted portals, and labyrinth. Its labyrinth should not be confused with a maze intended for entertainment: it was a symbolic devotional feature set into the nave floor.