Serafín's place was great!
Perfect location in Casco Viejo. 1min walk to Mercado de la Ribera, which was a perfect spot for espresso and tortilla in the morning, and about a 25-30min walk along the river to the Guggenheim. And the street is quiet at night, despite the seemingly endless bars for pinxtos and drinks all around.
The apartment was clean and well-stocked with a comfy bed. Serafín and his co-hosts were friendly and responsive, and even accommodated our late arrival and departure times. Recommended to anyone visiting BIlbao!