Could you post your dates in May?

There might be a festival in an easy to reach location you could go to.

Out of Zaragoza and Valencia (both of which I've been to) I'd definitely suggest Valencia. Great buildings - old and new, wonderful markets, and an unbeatable atmosphere in the evenings and, especially, at night.

Zaragoza is certainly a pleasant city, but a real highlight there would involve travelling by car for the 70 miles it takes to reach the magical Monasterio de Piedra. http://www.monasteriopiedra.com/defa...px?info=0000D5
Not so easy to do if you're travelling by train.