I would suggest some random locations, passes, etc: Vrsic pass, riding to Mangart is also great, Bovec (maybe try some white water rafting?), then move to Croatia, where you can stop at my place ( Lobagola B&B | design bed & breakfast in the center of Zagreb) to grab a cold  and we can chat using the map to route your way over Balkans  .
In Croatia a must see are Plitvice lakes National Park, and I would suggest to ride over Zumberak mountain, loads of twisties  .
From Plitvice lakes you can venture to Bosnia and visit amazing little town Bihac, nearby which is famous abandoned air stripe at Zeljava.
I would not skip Bosnia if you are already in Croatia but if you give us more info about time available to do the ride I can be more precise with more suggestions.
Cheers
Dooby
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