Syntagma Square is Athens central square. The name of the square is derived from a an uprising on 3 September 1843, of the people and of the guard of Athens before the then Royal Palace building, (what is now Parliament), demanding that King Otto grant a Constitution (Syntagma means Constitution), Syntagma Square and Omonoia Square are the two central locations of the city. You should not be surprised when you ask directions if people refer to Syntagma square. Plaka, the Acropolis, the Cathedral, the National Garden, Ermou str. and Kolonaki, are located in the vicinity of Syntagma Square. You will find fashionable cafes and small restaurants located here. The square is busy around the clock. At the kiosk you will find miscellaneous items, ranging from aspirin to souvenirs, newspapers, and foreign magazines. Text from free copy national tourist guide                                    
TIPS :
1. At Syntagma square you can find: Sub way metro lines terminal,  tram line terminal, happy train to see the central town, sightseeing colored busses and many normal bus and trolley stops to go further.
2. Tranfer to Nestorion from Syntagma:  Embarkation Bus B2 near the tram terminal. Disembarkation: Bus station "Onasseion" (end of Syngrou avenue). Tram line 3 to SEF Disembarkation : "Agia Skepi" (takes long time) https://goo.gl/maps/sWd2X
3. See album of Syntagma square in our fb.