if you go to Venice you can take boat to Pula (country Croatia) my town. 1 hour by boat from Venice and you won't be disappointed
Might as well travel to Bari, take a ferry to Patras, and work your way backwards. He'll be able to hit some other greats sites and visit Croatia on his way back. I haven't tried this myself, so he'll have to look up where the train run on the other side.