The apartment really is utterly charming, just as everyone has already said. It has character, and feels really homely - not at all sterile or anonymous. We really appreciated the little extras that you don't always get: a real teapot - and real tea! A lot of the basics for cooking, and decent knives. And an air conditioning unit - essential, even in September. It's obvious that a lot of thought has gone into furnishing and equipping this home from home, and all to a very high standard.
Paula was extremely helpful too: when we once had a small problem with the washing machine, it was solved within an hour, and she was most obliging and accomodating when we arrived earlier than was really convenient for her.
There's a rather surprising view out of the window: a blank brick wall. Now this might not be picturesque, but it has the great advantage that the flat is not overlooked at all, so you can open all the windows without worries. The street has virtually zero motor traffic, but don't expect complete peace and quiet: Madrid doesn't sleep, ever.
The location could hardly be bettered: so convenient for Prado, Thyssen-Bornemisza, and also for the Huertes barrio with busy bars and restaurants, tapas and raciones, and there are plenty of little supermarkets or fruit and veggie shops, and the Mercado de Antón Martín is a short walk away. And if you want some fantastic bread, there is an amazingly good bakery in the other direction: follow Calle Fúcar North; it turns into Calle de Jesús. There's a bakery on the left just past the intersection with Calle Lope de Vega. Food, good food, is never far away.