The “core” of the historic centre is the Plaka neighborhood (at the eastern side of the Acropolis), which has been inhabited without interruption since antiquity. When you walk through the narrow labyrinthine streets lined with houses and mansions from the time of the Turkish occupation and the Neoclassical period (19th c.), you will have the impression of travelling with a “time machine”
http://www.visitgreece.gr/en/main_cities/tour_in_the_historic_center_of_athens