Staying at Marta Y Gerardo's place was amazing. The place is so big you can't imagine it from the pictures and the two terraces are amazing. The views are incredible. It's very close to Plaza Mayor, La Latina and Sol, you have all the brunch, lunch, cafes and dinner places around the corner. The neighbors are also nice and chatty.
The flat is on the 5th floor, the elevator only goes to the 3rd floor, but that's not a problem, or at least it was not for me. It had two bathrooms - which were too much for me as I mostly stayed there alone - but I am sure it comes in handy when more people are living there.
Great staying at your place and I will check this place when I will be back in Madrid.