It is possible for you to start your travel from a country which is not your home country (your country of residence).
If you live in Poland, you could, for example, take a flight to Spain, and then start your train travel. However, the flight ticket would need to be purchased and paid by you.
However, you can receive a ticket to fly to insular countries (Malta, Cyprus and Ireland), if you request it to the Travel Team via e-mail firstname.lastname@example.org. Places are limited and booked based on a "first come, first served" basis.