There are many trains daily for Corinth from Elefsina, and even more if one is heading to Isthmia because extra trains branch off there for Loutraki. The Plain of Megara is a cultivated region planted with olives and grapes. The city of Megara (pop. 25,000) is a big country town rising on the slopes of two hills, each just under 300 meters high. From here, the rail winds up into the Yerania Mountains, passing through tunnels, and with spectacular views of the Peloponnese.
This area was the natural boundary that protected Corinth from Athens. The train descends into a plain, with a stop at Aghios Theodoros, on a long sandy beach, the station a few hundred meters from it. The area is known for its candied fruits. The rail line continues across the Plain of Sousaki, an area that rather oddly combines oil refineries and tank farms with great views across to the mountains of the Peloponnese.
Then it climbs to the station of Isthmus, where the line splits, with one branch going off to the beach resort of Loutraki and the other heading over the Corinth Canal to the Peloponnese. The Isthmus of Corinth is a barren limestone strip 16km/9.92miles by 6.5km/4miles wide. The ancient Corinthians developed a paved and grooved track, the Diolkos, on which ships were dragged across by a winch between the Bay of Corinth and the Saronic Gulf., a system used until the 12th century. Parts of this mechanism are still visible at Poseidonia (on the Bay of Corinth side). Work on a canal was begun in AD67, by Nero, but was halted due to an insurrection in Gaul, and the task waited until 1881-1893, when a French company resumed. The canal, cut 87meters through the rock below the surface of the isthmus, is 6.5km long, 25meters wide, and 8meters deep, with breakwaters on either end. Through it pass large ships, ferries, and cruise ships; the canal made Piraeus into a major port. It also had an effect of the railways, when the coastal shipping lines changed to steam during the 1930s, and one could travel much faster to the Ionian islands through the canal by steamer than by taking a train from Piraeus to Patras.
The competition forced the railways, however, to switch to diesel equipment, which shortened the travel time considerably-to about four hours, which is about how long it takes today. There are many cafes, restaurants and shops in the canal area, for those who find the canal of interest, as well as ancient Isthmia, with its Sanctuary of Poseidon, and the site of the Panhellenic Isthmian games (near the village of Kryavryssi). There's a museum there as well.
Loutraki , 6km from the Isthmus, is a beach resort, and a producer of bottled mineral water. It also has thermal spas, hydrotherapy , and a casino. The Lake Vouliagmeni lagoon near Cape Melangavi can be visited from here; ancient Perahora is below the modern town on a small sandy cove.
Corinth, the train crosses the Canal at slow speed, for best viewing. Most trains continuing on from here stop to exchange crews and/or divide the train, so there's time to get out and stock up on whatever.