Millennium Bridge (cool!) from Newcastle is the Baltic Art Centre in Gateshead. It is a simple, fun, contemporary art museum. It had a whole floor in tribute to John Cage, with a mix of his visual and audio work, but its most striking exhibit was "Doubtful Sound" by Cornelia Parker, which took up almost a whole floor by itself! It is exhibited marvelously, so you can look at it from a balcony, but then you can also examine the crushed instruments up close - it was an exciting experience.
But what captured my daughter's interest the most was a curious contraption in the back of the children's area -- a simple triangular cylinder that is mirrored on the inside, and is large enough to crawl into. She found it endlessly entertaining -- I'm tempted to try to build one at home.
Oh -- and the baked potatoes in the cafe were amazing!