Spain
Now
that the IP1 motorway is completed with a bridge across the river it is
quite possible to visit Spain for the day. The nearest large Spanish city
is Seville with its typically grand Moorish architecture including the
Cathederal and the Giraldia Tower, tapas bars and massive air conditioned
department stores (El Corte Ingles is very impressive).
The other city that you may consider visiting is Cadiz on the coast in the heart of Sherry country where the seafood restaurants are among the finest in Europe.
If you decide to go to Spain you will need your passports and car hire documentation though thanks to the common currency pesetas are no longer required. Remember that there is an hours time difference and Spanish mealtimes are later than in Portugal.