Thanks to everyone for the suggestions - looks like we will most likely stop over in Valencia.

Right decision, in my view! Although Seville is great for New World connections and Muslim past (Columbus is supposed to be buried in the cathedral), Granada for the Alhambra (the most beautiful Muslim palace in Europe) and Tarragona for its Roman heritage (Pontius Pilate was born there), there's nothing outside of Madrid and Barcelona to beat Valencia.

Make sure you buy a Tourist Card from the information centre at the airport (or at others around the city). This allows unlimited travel on the metro (i.e. subway) and EMT buses for the number of days you have purchased - and includes some shopping discounts, too.

Valencia airport is conveniently connected to the city by metro, which is fast and safe.

With so much to see and do in Valencia (are you interested in seeing the Holy Grail from the Last Supper?) it would be best to work out what you want to do beforehand!

I adore Valencia and visit it whenever I can.