Once a cathedral, once a mosque, and now a museum, and perhaps the most beautiful building in the world.
I think that the loss of the cathedral due to protestantism's opposition to the extravagances of the Roman Catholic and Eastern Orthodox Churches has led to a world where art is almost reviled by Christians, and in turn we have crude small churches lacking in pipe organs and art. Many lack any iconography as well.
I think this has led the Christians further away from God, because I believe God and art are closely related. What should have been spurned in the old churches was the lack of religious tolerance and hypocrisy.