A very disappointing stay. The check-in is not intuitive: the pre-checkin paperwork (which was "required by law", but strangely not required by any of the other places we stayed) was quite annoying, and to enter the building you to have a fully charged phone with data (not always the case after arriving in a new country!). The walls, as others have said, are extremely thin. I could have a conversation with the unit next door without raising my voice above speaking level (street noise was OK, except for Monday night when the next block becomes a street party from 10pm-4am).
My 1 star review is because we rented the unit because it had two beds, yet we arrived to find there was no bedding at all for the second bed. We immediately contacted the company to request bedding, and were told it would be right over. Then we got a message saying that they couldn't deliver bedding, because it was a Saturday and no one was in the office, and it was OUR fault we didn't have bedding because we didn't tell them we would need both beds. My family runs an airbnb, and to not have someone on call for necessities like this is absolutely unheard of, in addition to providing bedding for all advertised beds. As they are a company handling multiple units, I was shocked no one was available at 15:00 for this reasonable request.
I was told we would get bedding the next day, which we did not, and only received it after I filed an official complaint. So, one of us spent two of three nights wrapped in (unclear if clean) blanket, on a bare mattress, with a pillow without a case. The service and treatment we experienced here was the worst of any airbnb I've stayed in. I recommend looking elsewhere for your Barcelona stay.