This place is far worse than one would expect after seeing the listing here on Airbnb. It is a basement flat, even half a floor below street level. It has two windows to shafts, one of those in the bathroom, and a metal-grilled window and door leading to a small terrace. So daylight is very limited. The metal door to the terrace is stuck and can be opened and closed with massive force only (my girlfriend could not manage on her own).
The bedroom is tiny. It just fits the relatively small double bed with about 20-25 cm space on both sides of the bed. It has a sliding door that can hardly be closed. But you likely don't want to close it as the room has no windows, nor any other ventilation. The bed is cheap and squeaky as hell, if you turn in the night you can be sure that you and your partner wake up. The light in the bedroom was only working intermediately.
The bathroom is not in the nicest condition either, the shower try looks quite unhygienic. We also had the unfortunate encounter with a medium-sized cockroach in the apartment. We also noted a disgusting smell in the apartment that improved a bit over time but never got away completely. The blinds etc. in the living room are quite damaged, everything feels worn out.
When trying to use the electric radiators in the living room one of them had a loose connection and the plug started to melt.
Upon arrival the terrace was full of rubbish and glass. Apparently neighbours above had a party and threw stuff down. Parts of the glass splinters stuck to the terrace, so it did not look like it happened just the day before but must have been a while before we checked in.
Isolation is terrible as well which is probably quite common in old buildings in Spain. But in the flat above the living area someone seems to be using a tumble dryer from time to time and if that is running it feels as if the building might come down any moment.
The only positive aspect was that David & Nani were very responsive and tried to help with the issues. For example they immediately apologised for the smell, the dirty terrace and the broken radiator plug, and offered to send the maid to check and clean the next day. However, this does not change anything about the fact that the place is much worse than advertised and totally overpriced for what it is.
If you want to spend a nice time in Barcelona avoid this place by all means.