By landing to Athens Airport (ATH) you can pick the Metro Blue Line (Airport Station) and stop over in Syntagma where you can change line by picking the Red Line with destination to Agios Antonios. You stop over in Omonia Station where you change line again by picking the train (Green Line ) Kifissia-Piraeus whith destination the Port of Piraeus. Form there you can pick the Ferry by walking from 10-30 minutes depending which Ferry you booked (High Speed or Conventional).