Hej hej ...
Here is some help:
Have a look on the train schedules
, the easiest way to find connections: https://en.rail.cc/interrail-train-connections
Then some links with more information about special trains:Zagreb - Venice
by night train: zagreb-ljubljana-venice-night-train-t1389.htmlVenice - Milano - Ventimiglia - Nice
by day trains. Attention to Italian supplements: https://en.rail.cc/italy/interr ... plement/it
In Nice stay here: nice-france-hostel-t2830.htmlNice - Barcelona
: nice-marseilles-barcelona-train-t3420.htmlBarcelona - Madrid
: do it by day train. Fast connections. Attention supplements: https://en.rail.cc/spain/interr ... plement/esMadrid - Porto
And if you like this help, buy your official InterRail ticket via https://interrail.rail.cc
to support all our work and the forum. Thank you...
All the best and have fun, Peter