This is a spacious, well-equipped apartment close the centre of the city. It's on the top floor, directly opposite the Guggenheim and must have the best views in Bilbao! The gallery and the city centre are across the bridge while the old town and the local centre of Castanos are nearby on the apartment side. The apartment is stylishly decorated with two bedrooms (one double bed, two twin beds) a living room area, well-equipped kitchen and dining area and a bathroom. There is a small balcony that you can fit a chair on. There is no air conditioning so you need to keep the windows open in hot weather. There are main roads nearby which can be quite loud at night. Macarena is a great host and can get you settled in well.
I would recommend this apartment for families with sensible children - it is high up with windows that open fully. If you are not comfortable with heights or enclosed spaces (the lifts are quite small) then this listing is not for you! While there is a balcony it can only be used by one person at a time.
Top tips - if you are staying for a while and want to use public transport get a Barik card (3 euros) to charge up with cash for cheap travel (you only need one per family); the Old Town Plaza Berria is a great place to try out pintxoes; the nearby Funicular de Artxanda takes you a great viewpoint above the city; the nearby Funikularekko Plaza has local shops and bars where you can get away from tourists; the Guggenheim is quiet from about 3pm onwards; the Bilbao Art Museum has a better collection and is free 6pm to 7.45pm each day. The beach of Plentzia is great and is about 50 minutes away on the metro.