Basque country is arguably the best place to eat world wide. Depending on budget, Arzak (three star Michelin) Akelarre (likewise) and just as good but resigned to the stars fanfare zuberoa. Also you must go to the old part of San Sebastian for pintxos, and if possible go to Astigarraga for cider tasting and the typical menu. If you know locals try to get invited to a sociedad gastronómica, which are private places, like a club, where the members will cook their own dinner. An incredible and unique experience.
By the way, everything I mentioned is around San Sebastian or Donosti in Basque, but you would find similar places in both Bilbao and Vitoria. Enjoy!