The flat is fantastic. Even though it is a bit small, it is very well designed and uses every space in a very clever fashion.
The flat was also super clean, the location is ideal, as you are a few minutes walk away from many of the main touristic spots.
Also; very important: THE BED, it was one of the few flats in Madrid that I could find with a normal double bed (and not 2 singles put together).
Definitely recommend this place and would stay there if available next time.