Yagos' appartment is quite well situated in the Exarchia area, in downtown Athens. You can go by foot to the Acropolis or the national Archeology museum (which we did).
The appartment by itself has 1 room and 1 living room. It is very convenient, clean and beautifully decorated. Most of all, it has an amazing terrasse, full of plants, very nice in the evening or in the morning.
Yagos himself is very kind and helpful. He gave us directions for our trips, some hints on Athens and indicated a very nice (and organic restaurant for my birthday.
Last but not least, he is totally fluent in French (i.e. : "Yagos parle couramment francais et travaille comme traducteur!").