The place was great. It is in a calm street near the Guggenheim Museum and the old city of bilbao. You can reach the apartement very good with public transportations (there is a Station of the airport-Bus not far away). The place itself was clean and comfortable and Sergio provded us with a map and a little digital tour-guide of all the interesting parts of town. Furthermore he was always available if we had any questions.
I would recommend this place and definitely stay there if I ever visit Bilbao again.