Elena and Sergio have a lovely, well equipped, well laid out apartment in downtown Madrid. Walking to Plaza Mayor was 5 minutes and to the main museums, 15 minutes. Elena was easily available for our check in and we were even able to get in a few hours early, which was great after an overnight flight.
The only negative was that there is a window in the bedroom, high in the wall, that faces a corridor that has a light which turns on when ever someone walks along. It was not a problem all night but there were times after we went to bed that there would be light suddenly for a few minutes. It will be much less of an issue for those on Spanish time and up later.
Otherwise a great place to stay.