Overall a very good stay in this apartment.
Pluses: Very central - in a small side street a minute's walk from the Metro and from the Gran Via. Clean and well equipped (everything as advertised), newly renovated. Spacious enough for two people to stay there comfortably. Quiet, even though it is in the center of the city and close to some very lively neighborhoods. Also, the communication with the host went very smoothly and they were accesible and helpful when needed.
Minuses: all the windows look onto a tiny internal coutryard which is not private, so the curtains more or less need to be drawn all the time, and there is not much natural light. Also, there is not much ventilation, and as a result the apartment is somewhat humid and has a somewhat musty/moldy smell. A dehumidifier is actually in place and is constantly running, but it does not seem to solve the problem completely.