Core: location is great, apartment will suit couples or 2+1 families and younger people rather than big families. The owner is responsive and reacts promptly.
Arrival. The address was clear and the owner's recommendations helped us to arrive with no issues. Antonio was there to meet us, even though we arrived earlier.
Outside. In the walking distance from all the key points in the city center, plenty of coffees, supermarkets and transport options around. The street is not very noisy if the windows are shut, but the garbage trucks come around 1am and are rather loud.
The apartment is on the 1st floor, but it was relatively high. Elevator goes from the ground floor - very convenient with trolley / luggage. The insides are spacious. A large kitchen, huge living room, 1 fair bathroom, a nice master bedroom and small 2nd bedroom + 2 lumber rooms. Antonio kindly provided us with a cot and a baby chair for free.
The kitchen is large and contains of the necessary stuff (not the dishwashing machine). The washing machine had mold inside - we reported to the owner, Antonio tried to fix this but was not able to eliminate it, thus we decided not to use it.
The living room has plenty of space for dining and relaxing. It even has 2 small balconies.
The master bedroom is large, has plenty of storage space and looks out to the tree at the little square.
The 2nd bedroom is smaller but also has enough storage space. It is located inside and does not have a window. The walls are thin, and you may easily hear what the neighbors are talking about if they aren't whispering. This only refers to this room and the bathroom.
The bathroom is equipped with a shower and has enough space and light. The towels were not new but clean.
To summarize, the apartment is a good option for your stay in Madrid - especially for a bunch of friends or a small family.