This city has been lucky enough to have been touched by an amazing artist called Antoni Gaudi - various buildings, parks and squares were designed and built by him during his lifetime in the late 19th and early 20th century. I was lucky enough to check out a number of them - the highlights being Park Guell and his unfinished church, La Sagrada Familia.
Under construction since 1882 (expected to be complete in 2026), its complex architecture is both baffling and beautiful - each pillar, facade and vault is an individual meant to reflect nature. It really is the most unique religious building I've had the pleasure of witnessing - and though it is more of a spectacle than a spiritual home, its wonder is certainly not diminished.
I took a video from inside its nave, my happy memento, that's more hilarious than informative but I hope you'll enjoy it anyway. If you want to see some more of what it actually looks like then head here: http://www.sagradafamilia.cat/docs_instit/images.php