Barcelona is home to Gaudí's Sagrada Familia Cathedral. Never in my life have I been so in awe of a church. I squealed at first sight.
Of course I've seen it and read about it my entire life, but seeing the Sagrada Familia in person was unlike anything I've ever imagined, much less seen. It's other-worldly. (I felt the same way about the Eiffel Tower).
P.S. Doesn't it remind you of a sand drip-castle?