Some advice :
Reservations within Spain are best done at a RENFE ticket counter. Remember that you can only use 2 pass days in your country of residence (not extra days).
The TGV between Spain and France is very expensive (27€ just to cross the border) and extremely popular : some July dates are already sold out. As an alternative take the reservation-free route via Portbou.
Seat reservations in Italy : 13€ Frecciarossa, 3€ IC → best done through tickets.oebb.at (no booking fee)
It is not possible to travel by train further than Zagreb or Split so you’ll have to rely on buses. Alternatives :
- Zagreb - Budapest - Bucharest - Sofia + bus to Thessaloniki
- ferry between Italy and Greece