Centrally located, easily accessed from Piraeus port and Athens airport.

Airport

There is a direct subway line from the airport to Syntagma square every 30 minutes, taking about 40 minutes. A single ticket costs  10 euros.  Alternatively, there is a bus line X95 just outside Arrivals terminal every 20 minutes, taking about 1h6 minutes. A single ticket costs 6 euros. Taxi stand is just outside Arrivals terminal, the trip takes about 30 minutes and it costs between 50 and 70 euros.  

Piraeus port 

There is a direct line (line 3) from the port of Piraeus to Syntagma, taking about 20 minutes. Subway station is across the street from port exit E6. The ticket costs 2 euros. Taxi stands are next to ferries upon disembarkation.