Doesn't sound super fast lol, but fast for Greece! So that's the bright sideSorry the only time I used a train in Greece was Metro in Athens . Others have told me about the train, apparently a fast train but it can't be that fast if it takes 4 hours to cover the 500 km. I usually pick up a car at the airport and use that for our stay in Greece, I even take the car of Ferries, most rental companies will not allow that. I use the same mob every time and they allow as long as you tell them what islands you are going .
If you have some time and you can drive, rent a car and go to Meteora, a Unesco listed monastery, it is not far out of the way.