What a beautiful space. If you are looking to be away from tourist land, and live like a local...Mercedes' apartment is perfect for you. Located within a 5 minute walk from atocha train station, this room allows you to go anywhere via walk or metro. The apartment is as you see in pictures. Highlights:

Location: close to the train station and around the corner from Prado Museum and Parque Del Retiro. You are also close to Calle de Jesus which is full of some of the best tapas bars in Madrid outside of Puerta Del Sol area. It was an easy walk from train station, but there's not much nightlife within the block of your apartment. Regardless, I liked the quiet, and walked everywhere.
Room-Clean, comfortable bed, but a bit warm. Without AC, it felt stuffy at night. I had to open the window, but since someone was smoking nearby, I had to close it. If you are coming in the dead of summer, the heat maybe a concern. The bathroom is modern and clean with good water pressure. Wifi is great, and the building is safe. Can be a bit dark at night, but just get used to the light switches. If you open the windows, there is a nice breeze, just hope no one is smoking.
Host-I interacted with Mercedes once. She was responsive, but I didn't see her much due to the nature of her schedule. It was fine, and I had much more interaction with the other room mate staying there-Camila.
Keep in mind there are 2 guest rooms, so you will be sharing the space with another stranger that has been vetted by host.

Overall, this place would be awesome if you like sharing a space with another AirBNB'er and want to be close to the museum district. It's quiet, safe, and really central in location. Only downfall is no AC.