This property is a 5 out of 5 and highly recommended. It is exactly as advertised and is very clean. We travelled with our 12 and 14 year old boys and they had a blast in the pool. We experienced no lag or internet issues despite gaming on multiple iPads.
The hosts were incredibly generous and very responsive to our questions.
We did not have a car, but everything is walkable and the metro takes about 30 min to get to downtown Bilbao. Taxi to the Abando train station in Bilbao was just under 45 Euros and the metro about 1 Euro each way. The Plentzia beach was nicer (or equivalent) to San Sebastián, with mainly locals not tourists. Plentzia is hilly.
Thank you to Regina and Sabin for ensuring our 4 night stay in Plentzia was the highlight of our Spain trip so far!