Great location, walking distance to Prado museum and Retiro Park, near metro station and train station. But be careful if driving: better to study beforehand the access and parking restrictions. We drove into a zone which was off limit to non-residents and we expect to have to pay a fine. There's a covered parking lot close by. You pay €20 per day.
The apartment can sleep six if you use the sofa bed and the double bunk bed. Apartment was really clean. Sleeping on the sofa bed, we could hear the sound of passers-by.
Very clean, everything worked.