Natacha is a great Hostess. She was very nice and helpful during our whole stay. For example, when we asked her for a kettle, on our first day at her place, she brought us a new one the very next day.
The apartment is small but more than sufficient for a single person or a couple. It has everything one might need during a short stay. Since Madrid is considered to be a very noisy city we were pleasantly surprised that the neighbors in the building are quite and considerate.
In general it is a nice apartment to stay in during your visit to Madrid. However, the mattress is very soft so it might not suit people with back problems. Also, the hot water runs out quite fast and takes relatively long time to hit up again.
The place is located right next to a Metro station and 15 minutes walking distance from the main train station and many tourist attractions. Despite its advantages and central locations the area doesn't feel safe, especially after dark. The streets tend to be empty while the metro station is often surrounded by shady looking people. However, it should be noted that nobody bothered us during our 5 days stay.
All and all we enjoyed our stay at Natacha's place.