We had a lovely stay at the apartment!
Since we arrived late at night (after 10PM) we had the option to pick up the keys from the nearby bar, and it was very helpful.
The apartment is well equipped, there wasn't anything missing or malfunctioning, and all in all we were very comfortable.
The location is great, although the climb to the 4th floor was exhausting.
We were delighted to stay at the apartment, and we will remember it fondly as a good part of our trip to Madrid :)