how would you get away from Patras? I assume the line to Athens is not finished?
The line is still some way off being finished. It's currently a rail replacement coach service to Kiato and then an electric unit from there into Athens.
The new line is open (unelectrified) as far west as Aigio, but there aren't any rail replacement services bridging the gap between there and Patras - although I suppose you could get a taxi or (if you trust what Google Maps says!) there are coaches to the bus station every few hours. However it's worth noting that the train station is quite a distance from the bus station.
I'm planning to return to London from here in Patras, Greece to London next week.
I normally take the ferry to Bari, Ancona or Venice but was wondering this year about going 100% by rail. I also want to visit Zurich on the way....
Interrail pass probably makes sense but not sure how that works in Bulgaria and Hungary.
Any thoughts are welcomed!
I did exactly this journey last year (having taken the ferry from Bari) - see my threads
here and
here. Unfortunately, there are currently no international rail services to/from Greece - they were withdrawn at the start of Covid and haven't been reintroduced. And as above, Patras doesn't have a rail connection to the rest of Greece (the local narrow gauge network is isolated).
The closest you can do to making the entire journey by rail is Kiato - Athens - Thessaloniki -Strymonas - taxi/hike (if you're very adventurous!) - Kulata (Bulgaria) - Sofia and then onwards. From Sofia, I decided to travel via Ruse, Bucharest, Budapest, Munich, Frankfurt and Brussels - but you do have a few alternative options, particularly so once you make it to Romania and then Hungary. Going via Zurich would be eminently doable.
I would warn you though - it's not by any means a quick or convenient way of making the journey - although it's certainly scenic for several sections. Despite using a sleeper (Bucharest-Budapest) and getting up at the crack of dawn on several occasions, it took me from Tuesday until Sunday to make the journey.