The railway line from Athens to Kalamata is one of the more scenic train rides in the Peloponnese, winding through countryside, small villages, and mountain passes on a narrow-gauge track. The route passes through Corinth, Argos, and Tripoli before descending to the Messenian plain.
Service has been intermittent over the years due to funding cuts to Greek rail, so check current schedules with OSE (Hellenic Railways) before planning your trip. When running, it's a relaxed alternative to the bus and far more interesting than the motorway.