Stelios's Apartment is newly renovated, super clean and near Syggrou-Fix Metro Station. I've read other reviews about the street noise, but it did not bother me the slightest. I even slept with the window slightly open.
Stelios himself was friendly, communicative and discreet. Thank you Stelios! I recommend the apartment for everyone visiting Athens for a couple of days or even for longer stays.