Josetxu's place is highly recommended, right in Casco Viejo with amazing bars and restaurants. Its a few minutes walk from the metro or about a 20 mins pleasant walk to the city/Guggenheim. Its also a few mins walk to Mercado de la Ribera. Although it can get noisy at night from drinkers/people below, its well worth it. The place is clean, has 3 comfortable rooms, with a functioning kitchen.