You will not find a better location, a more comfortable apartment, or (most importantly) a better host than Paulo, one of the most welcoming persons I've met anywhere.
Paulo went to the trouble of meeting us in person immediately upon our late-Friday-night arrival to give us keys and to orient us to the accommodations. He also supplied endless suggestions for attractions and dining in Madrid. We reached out to him perhaps excessively for several needs, and he was immediately responsive with the most helpful support we could ask for.
The apartment is in a perfect location, within walking distance of every must-see Madrid site on our list. Other comments here noted the noisy location, above a pedestrian mall. However, we loved staying on a street that had almost every imaginable amenity. Additionally, we found we could shut out the noise at bedtime by simply closing the floor-to-ceiling windows and shades.
North Americans may find the space small in comparison to typical US and Canadian apartments, but it was more than adequate for our needs, especially the large kitchen, which was fully equipped including a washer.
I would stay here again without a shred of hesitation and can't give Paulo enough praise for his exceptional hospitality, including fluency in English, Spanish and Portugese.