We stayed in Bilbao for one week with my wife, 3 years old daughter and 6 months old son. I’m not sure anyone mentioned it before, but there is fairly narrow staircase leading up to the apartment, so if you’re traveling with stroller, be aware of this small nuisance.
The location was great, old town, walking distance to any point of interest. Beds were comfortable and apartment was stylish.
There were couple of minor issues, which we communicated to Iñaki, like blunt peeler, broken lightbulb and freezer covered in ice. Also bathroom was a bit smelly. Hopefully these will be resolved for the benefit of future guests :-).
Bear in mind there is no washing machine in the apartment, we didn’t notice that when making a booking, so we had to use a public laundromat on the same street.