Join Date: May 2006
Location: New York, London, Sydney
Programs: United GS/2MM, DL*P, VS*G, AA*EXP, Avis CHM, Hertz Platinum, Sixt*D, HH*D, HGP*P, Starwood*P
Posts: 9,847
You're talking at least 39 train hours, one overnight, and 5 trains. As far as I'm concerned, you'd have to be completely out of your mind to do this.
That having been said.
Prague-Budapest
Budapest-Bucharest
Bucharest-Sofia
Sofia-Thessaloniki
Thessaloniki-Athens
would be the routing.