This was a great little place for my solo weekend in Madrid -- it was within walking distance to all the places I wanted to go, around the corner from Chocolateria San Gines, and also not far from the train. Julia was a great host, helped deal with a flight delay so that I could still check in, and even allowed me to leave my bags in the apartment after I checked out.
As other reviewers have noted, this is a small place and there is no door on the bathroom, but it worked great for me. It got pretty warm in the summer in the bedroom area in the back, but they did provide a fan which helped. There's some construction going on in the building so the foyer is a little scary in the dark, but there was an elevator for luggage.
It was somewhat complicated to get to/from the airport from Sol, since you have to take the Cercanias to get to a station with the metro to the airport, but I recommend getting the 8euro "tourist ticket" which covers both.