Passes are for personal use only. The cheapest pass to go to Croatia is a 4 days (within one month) pass. Choose a route through Germany (avoid Thalys) and Austria to avoid expensive mandatory reservations.

Please note that it is a 15 days Pass and not trips! You can change trains in one day so much you want. 

Please note also the nighttrain rule. When you take a train that arrives at destination only the next day, you use only the day that you start. A nighttrain to Croatia is from Zurich via Feldkirch to Zagreb. There is also a service from Munich to Zagreb, but only on some periods of the year. 

You could take a ICE from Brussel to Frankfurt (no reservation needed, but you can) and than change on a ICE to Zurich (no reservation needed). In Zurich take the nighttrain to Zagreb (reservation needed??? I think you need a reservation for couchette or sleeper cabin, for a seat I don’t know → book reservation on tickets.oebb.at or with additional fee on interrail.eu). If you whant to go somewhere else, take a bus, buy tickets for the next train or use an other travel day on you pass. 

Look also if you take only day trains on bahn.de they have good cheap (Super) Sparpreis Tickets to Croatia. Every day there is a EC from Frankfurt/Main to Zagreb via Munich if you don’t want to change trains. 

Another option to go to Croatia could by saverfares of German or Austrian rail for example

have a look on oebb.at and bahn.de (you could try the entire way or split the Route in two halfs )


With Interrail it´s possible to travel in one Travelday to Zagreb or Rijeka
Belgium - Cologne/Frankfurt (avoid Thalys)
Cologne/Frankfurt - Munich
and catch in Munich the Nighttrain to Zagreb with a through Coach to Rijeka the Nighttrain is reservation compulsory :/