3 words: heated Bathroom Floor!
Mark's place is easy to find, a quick walk from Waverly station, then up 3 or 4 flights of stairs. It is just downhill from the tourist-land part of the Royal Mile, close to Cadenhead Whisky Purveyors, close to the amazing David Bann vegetarian restaurant, easy walk to Univ of Edinburgh campus.
The apartment itself is modern, clean and comfortable with -- did I mention?-- Aaahh ...a heated bathroom floor. Shower and bath, enough hot water for a decent shower or a shallow tub bath. We stayed in a large, quiet comfortable room overlooking an open courtyard. Cereal breakfast.
Finally our host: Mark is a really nice guy!