Kristian's apartment is the perfect place to explore Madrid. It is within walking distance to all of the sights, and is very close to the main squares. We didn't get to meet Kristian unfortunately, but it meant we got the whole apartment to ourselves. He sent us excellent and detailed information in how to get to the apartment from the airport, and even some tips on places to eat.
We didn't spend much time in the apartment itself, but it was as described, with a well-sized room, bathroom and kitchen with everything we needed. It was quiet at night, as it doesn't look out on to a main road, which was great. The only slight negative was that the wifi didn't work that well for us - it was fast intermittently, but sometimes wasn't very good.