Overall, we were very happy with our stay. The location is great - near center, but away from main avenues, keeping some distance from the dense car traffic. The two bedrooms and living room are spacious and comfortable. The kitchen and bathroom are of smaller size, but perfectly sufficient and functional. By US nomenclature, the apartment is on the 5th floor, if the building entrance level is counted as 1st floor. When you open windows at night to get cooler air in, you may hear some chatter from the cafe-restaurant outside on the ground floor, but it is muted by the distance. We got hit by the heat wave (over 40 degrees C) during our stay, so we used the air conditioning. With the two window layers closed, the apartment stayed cool and quiet. It is pleasant to open windows early morning and enjoy fresh air. Regarding ventilation, the kitchen and bathroom have both a window to an inner shaft that seems to be open all the way up through the roof. However, it seems that the air from the kitchen of the restaurant is vented to this shaft, with smell of frying oil, so it is better to keep those inner windows closed.
Thanks to the excellent location, we mostly walked to galleries, museums and restaurants - there is plenty of the latter in the immediate vicinity, and also cafes and bakeries for breakfast. While we did not do much cooking, the kitchen is well equipped with a stove&oven, microwave and three coffee making devices (mocca pots & such). We missed a teapot type of vessel (with a spout) that would allow to pour safely hot water to make tea - doing it using the available metal kitchen pots was a bit awkward, but manageable - this can be easily fixed. Overall, we were very happy with our stay and would gladly reside in this apartment if we return to Madrid in the future. Communication with the host (before and during the stay) was excellent.