Just got back from Bilbao, place is amazing. It rained most of the time, normal for the time of year, but it didn't matter. Apart from the Guggenheim (which, unlike others, I think is a monstrosity of architecture) there's a range of museums, including the Bellas Artes (fine arts) one. The food (pintxos) is the most amazing thing about the place as well as the local wines (some say the whites are best, but I tasted some good red ones). You can't really go wrong. Plus, the people are friendly.