When Dan and I realized we had 5 and a half days to visit Spain after my conference in Barcelona in March, we immediately started brainstorming where else we could go. By the time Dan arrived, I would have already been in Barcelona for a week, and Dan was inclined visit other cities.
We thought about the South of France (Toulouse, Montpellier, or even Nice) but ultimately decided it was a lot of traveling for the short amount of time we had. Madrid would have been the obvious option since it was just a short 3-hour high-speed train ride away from Barcelona, but we also briefly considered Zaragoza and Sevilla. Ultimately, once we found out Valencia is the birthplace of paella, that made our decision.