I spent two weeks at Belen's place working remotely and exploring Madrid. The apartment is exactly as described in the pictures. The location is amazing: just a couple of minutes from Plaza de Santa Ana, while it's still a quiet street. I barely used the metro because it was so easy to walk everywhere.
Belen is super kind, communicative and flexible. For example, she provided me with extra pillows when I requested those, and brought a fan to the room (which is so necessary in the summer heat in Madrid). We wore masks in the apartment when we were in the same space, which is good to be prepared for. Overall, it was a good experience and I would recommend Belen's house for anyone who wants to stay super central and also have a cozy home to sleep at.