The apartment is great, lot or space, you can stay in 6 without any problem.
The position is also fantastic because you can easily reach the Airport (40min total considering bus+15min walk, but you can alternatevely take the metro instead of walking) and you are in the heart of the old city, full of restaurants, supermarkets, shops...
Guggenheim is 15min walk along the beautiful River that cross Bilbao.
Luis is very kind and let us the apartment full of beverage and food for breakfast, awesome.