The flat is overall very nice and practical. Nice furniture, good built-in wardropes, comfortable beds.
The location of the flat is absolutely great, very central, but facing to the internal courtyard of the block, so very quiet. We were impressed by Bilbao, not only Guggenheim, but the city overall, and the flat is a good spot, to explore the city from.
We had bikes with us and put them to the public space just opposite the entrance, which worked well. The neighbourhood is very clean and well maintained and we did not have fear that they were stolen. According to the tip of the agency, we parked our car at the car park of Plazza Euskadi, which worked very well (~13€ per 24h).
The only thing we found mot up to the same standard with the flat was not the kitchen itself (good fridge, oven, dishwasher, etc.) but the equipment with movable things like number/quality of plates, cutlery, etc. One can come by, especially of course with all the restaurants and bars around the corner, but we had e.g. to run the dishwasher half full, because there were too few e.g. plates awailable.
In any case, we would book the flat again!