I didn't see the Sagrada Familia. I didn't step foot in a single museum. The morning I planned to go to Park Güell, it poured rain.
I think Barcelona is best when you let it happen to you. You don't make plans but let your friends lead the way. Your first meal is sushi and you find yourself at dim sum the next day. (Don't worry, you get empanadas and churros con chocolate, too.) You forget to tell your first college friend you're coming to town but manage an entire evening with him (and new friends!) anyway. You find a tiny owl for your collection. You don't remember Spanish but can somehow hold entire conversations without English.
You know nothing about the city but find beauty and color everywhere.