Rowena and Thanassi are really nice. We had a couple of problems in the flat (nobody's fault) and they were amazing.
The flat is very well situated in on of the Kolonaki busiest streets, but it is very quiet as the windows are on the garden, very clean and pleasant... You don't have to climb on the Lycabettus hill to get there, as it is the case in many of the flats in the area, and it is very close to Syntagma, and then, to Plaka. Definitely recommand it