I would imagine if there's one thing you could find, it would be French medieval churches.
How about starting with the traditional burial church of the kings' of France, the Saint Denis basilica:
The stained glass of the Paris Sainte Chapelle is kind of impressive:
There's the cathedral of Chartres, peppered with mystic, neo-platonic apparently, symbolism:
The Notre Dame is of course a display of the politico-religious power of the French monarchy of the times:
The Abbey of Cluny, in Paris, incorporating Roman architetural remains, and today a museum of Medieval history:
If in Paris you could also check out the "Musée nationale des monuments francaise", which kind of impressively odd as a musum filled with 1:1 19th c. copies of important, mostly Medieval, stuff:
And that's just some Paris-and-environs-stuff.