Barcelona Cathedral of Saint Eulalia was built between 1298 and 1460 and it's a beautiful Gothic piece of architecture.
I was astonished when I read that the front facade was added to the building only in 1870.
It's a really impressive church, both from the outside and inside. You can also go up (in a lift :) and admire the views from the rooftop. I decided to go up and because I went there early in the morning, I was the only guest so I could enjoy a moment totally alone.