Sorry fjaka, but this is by viamichelin.com...

Diferent way is in your pictue, because he will go via Podgorica and Virpazar (Skadar lake), not via Cetinje...
On this, my picture, road goes arround Kotr bay, but that is not nesesery, and that is 30 km more than by ferry...
By viamichelin.com, road from Dubrovnik via Niksic to Zabljak, has 171 km...
