First was the Basilica of St. Louis, King of France, otherwise known as the "Old Cathedral," which is on the river, right by the Arch. It was constructed in the Greek Revival style. I could tell how old this place was-- built in 1834. I have to be honest-- not a ton to look at, but still very old, and very French.
Next up was the Christ Church Cathedral, a gothic revival structure built between 1859-1867. This was was truly beautiful, inside and out.Cathedral Basilica of St. Louis, which is supposed to be the best of them. I saw it as a kid, and I remember the amazing mosaics covering all of the walls. Next time, I'll start there.