This place is great in many aspects: It is located in the middle of Casco Viejo, so you are in the middle of the historic city center of Bilbao.
The apartment is spacious and well equipped: a very clean and great shower, a fully equipped kitchen with kettle, Nespresso machine, stoves, and oven, a big fridge and freezer to store your market hauls. There is a small balcony with an awesome view down to calle Jardines. The bedroom has plenty of closet and storage space, and the bed is really comfortable.
One caveat is that the apartment is on the third floor without elevator, but if that doesn't scare you, it is the perfect homebase to explore the city.
Ana and Iñaki were great hosts: Iñaki picked us up at the tram stop, and Ana went out of her way to give us valuable tips on what to see and where to get food at which time, so we immediately felt comfortable with the tricky eating customs of the locals :)