The good news is that train travel from Athens to the Peloponnese is improving all the time—or, at least, is scheduled to improve. The bad news is that extensive track work is ongoing on the Peloponnesian lines, service interruptions are common, and Greece’s financial woes have severely curtailed improvements. There are plans for a fast network to be running from Athens to Patras, Kalamata, and other cities in the Peloponnese, but no one is counting on such a network actually being in place soon. If you are traveling from Athens to anywhere other than Corinth, you will probably find bus travel to be faster, more reliable, and in many cases your only option for public transportation. Trains run to and from Corinth (Korinth N. station) and Athens every hour between 8 and 8. The trip takes one hour and costs €8.50 to and from Athens, €11 to and from the airport via Kato Acharnai Station. Tickets can be bought online or at stations.
Greek Railways Organization (OSE). www.trainose.gr.