AUTOBus. You pay. Is that really so hard to think of? ESpana also has a big network of ALSA and AVanza that covers about the whole country and is often quicker and cheaper as RENFE on secundary lines. In the past people bouhgt little guidebooks which had all these details-but nowadays there is a good friend, named google.

In GR all buses are green and by KTEL=a coöperative based by province. In Ath-from what I remember there are/were 2 major busstations where by direction these buses left from-much, much bigger as the small train estacion there. You do not have to sweat now for booking online-most tix are still simply sold at window right before dep. But informing more a day or 2 before would be wise

Obviously, my question is not how to arrive, but how to arrive with my pass, that is already payed. And, obviously yes, I do have a good friend named Google. Thanks for your help. 

The Greek rail network is quite sparse, many places have no rail and even those that do have a relatively infrequent service.