While in Paris, if you can, be sure to go to (obviously) Notre Dame, but also, not far, on the Left Bank, there is the stunning St. Severin, and also on the Left Bank, St. Germain de Pres. There are, of course more stunning churches in Paris than you could possibly visit in a usual short trip, but those are all historic so you get much more “bang for the buck” if you go to mass in one of them. On the Right Bank, there is St. Eustache, where Moliere was baptised.
There is also a beautiful English Gothic Episcopal (US Episcopal Church) Cathedral of the Holy Trinity on Rue Georges V down the street from Champs Elysees.
