Myself and two other friends stayed at Serafín's 2 bedroom place during the carnival season in Bilbao and we could not be more impressed with his place!
Although we had a tricky problem arriving there (as the taxi driver didn't seem to know where the appartment was located and this happened at least 2 other times), we were greeted in the street close to the apartment by Silvia and her husband who took us to the place and were incredibly helpful and super friendly.
The place is very modern and stylish and looks exactly as it does in the photos - the shower was my favourite thing in the apartment! Although not in the centre, all of the main places in Bilbao including the Guggenheim are in walking distance, or a short ride by taxi with the airport only 20 mins way by taxi.
Serafín was very easy to get in touch with and was in frequent communication with us weeks before we checked in with Silvia always quick to respond via text/whatsapp.
I would give Serafín 10/10 and highly recommended his place to anyone visiting Bilbao!