Please use the search option from this community When i search for Athens i can find a post from Yesterday with a similar question and many more in the last weeks :)

There is currently no International Train to Greece :)

Easiest Route is Train to Sofia then by non included bus to Thessaloniki and then by train to athens
Option B is a Ferry from Italy to Patras and then with inluded Bus/Rail connection to Athens :)

Easiest-by far- is fly. Try wizzair. even also direct to many GR isles in summer. Very big in HU.

But it is of course to the eternal wrath of climate heroes and a swedish lady named Gretha.