Oviedo has an amazing cultural and historical offer.  Oviedo Cathedral, built over three centuries  is well-worth a visit. Its treasures include the Victory Cross, the Holy Shroud, the Agate Casket... It offers audio guides in English. The Museum of Fine Arts, a stone's throw from the Cathedral,  is amongst the best in Spain, and has paintings from,  amongst others, Rubens, El Greco, Picaso, Miro, Goya, Sorolla... and the Unesco sites of pre-romanesque architecture are a must, right next to the statue of Christ with amazing views not only of the city below, but all the way to the coast in the north and the mountains of Aramo to the south.  

Oviedo old town is a great place to walk, full of pedestrian streets and squares with cafés, surrounded by iconic buildings and right next to the main shopping area (the 'Golden Mile') and San Francisco park  (a great place for a picnic).