Plaka is the heart of the Athens historical center and a popular place to meet friends, have a drink and dine.
Its probably the most charming area of Athens with old buildings and cobblestone pedestrian streets. It's adjacent to Monastiraki, but with many more quiet streets to explore.
While parts of Plaka have been traditional hot-spots of trendy restaurants and bars, many side streets are residential areas under the northeast shadow of the Acropolis with Ano (upper) Plaka being more residential and closer to the Acropolis and Kato (lower) Plaka hosting more commercial venues closer to the touristy roads between Syntagma and Thesion Stations.
Narrow roads that serve the residents criss-cross the cobblestone pedestrian streets, but otherwise traffic is severely restricted in the area. The area hosts numerous traditional bed & breakfast hotels that are usually on the pricey end, and several small museums, all wrapped around the archaeological sites of the Roman Agora.
Adrianou street is reportedly the oldest, continuously used street in Athens, having survived unaltered since ancient times.
Plaka's winding streets are perfectly suited for an afternoon leisurely walk. The winding streets and the quaint homes that climb precariously upwards to the side of the Acropolis giving it a "Greek island" sort of atmosphere. Some streets as you approach the Acropolis are steep but not too difficile to walk, but lower Plaka is mostly flat and a bit more comfortable.
Most notable of the museums in Plaka include the Kanellopoulos Museum that houses ancient and Byzantine artifacts, as well as the Center for Folk Art and Tradition and the Museum of Greek Folk Art. A small Children's Museum is a good place for younger kids, and the Museum of of Popular Music Instruments has a fascinating collection of instruments.
Other highlights include the Library of Hadrian ruins right next to Monastiraki Metro station, and the Roman Agora, both of which can be seen comfortably withing the period of one hour. If you hike all the way up to the root of the Acropolis rock, watch the numerous ancient caves carved on the live rock as you walk the path that circumnavigates the Acropolis watch