We stayed 3 nights in the appartment of Mercedes. It's in the old part of the city and we enjoyed the location very much, because it's nearby all the things we were looking for (restaurants, bars, sight-seeing). Mercedes was easy to reach, just like her friend, who welcomed us (and bought us even a beer across the appartment while we had to wait a few minutes longer before we could check in ;) ! The were both very helpfull by giving us advice where to go and to eat!
The appartment self is small, but just big enough for 2 persons. We had a great time in Bilbao!