We spent 6 nights at Charles' place. The location is really center, just above one of the most crowded shopping street in Madrid. 1 min to callao station, 3 min to sol station. Charles and his sister live in the room next to us so they are always reachable when we need help. The public space in the apartment is tight but the bedroom is big enough. all in all we enjoyed our stay at charles's and definitely recommand it!