Me and my family had an amazing time at Ruth and Oscar's apartment. They were very responsive to any question and helped us with everything we needed to know.
The apartment is VERY VERY good located. you won't find a better area to stay if you are looking to walk around Madrid.
Nicely decorated! Comfy beds. The place to book in a reasonable price.
The only thing is that there's no elevator and you need to claim 4 floors. Not bad at all if you want to eat lots of tapas!