Im going to visit Spain in Feb for my honeymoon. If I had one city to visit, which one should i go to?

Baracuda asked: I plan to stay there about two weeks. I like to visit museums, aquariums, planetariums, any interesting sight-seeing activities, I love the arts and culture, architecture, anything that’s interesting, fun and romantic. My friends suggested Madrid and Barcelona, but I might just be able to visit one. But which one?