I spontaneously decided to visit Madrid and booked the Room C for 4 days. the apartment is located in city district with many bootiques and is well connected. The house and the flat are nice, the room is clean and has a cosy bed, so I could sleep well at night and it has an ensuite bathroom with a shower, so I felt being in a hotel room:) I knew it is not big and doesn't have a window, but it has everything you need and it is absolutely enough for a short stay. One thing you need to consider is that the room is in the kitchen and you hear everything people do and talk there in the breakfast and diner time. It didn't bother me, because I was all the time exploring the city.
Roberto is a nice and very helpful host.