Chartres is famed for the 13 century: Cathédrale Notre-Dame.
This Gothic cathedral, completed in 1220, features 2 towering spires, flying buttresses, and elaborate rose windows. In its day it was the second largest Christian church in the world, after Hagia Sophia in Constantinople, and was among the most popular destinations for Western Christian pilgrimage during the medieval period.
It's nearly one-and-a-half times larger, and considerably more ornate, than its, now rather charred, namesake in Paris.
The stations of the cross are particularly elaborate
Obviously, the town is even older than the cathedral, yet there are few remnants of the medieval. It's mostly far more modern, with a plethora of church related infrastructure (convents, hospitals and so on) radiating out from the centre.