Il Duomo di Firenze, St. Basil's, Notre Dame -- every year, millions of pilgrims (not those guys who came to the US from Europe) pay homage to the most famous cathedrals in the world. Many are as beautiful as they are historic. These are not those cathedrals.
Just because a church is holy, doesn't mean its construction was a good idea. These are the ugliest cathedrals in the world.