Three snaps to avoid if driving from Northern Europe to Montenegro :
1. Croatian motorways: the roads are ok, but the tollgates are not. At least three hours waiting in Vrgorac.
2. The Sveti Stefan II ferry between Bar and Ancona. This is the worst ship of the Mediterranean Sea. The average temperature in the cabins is above 32°C (90°F), the rest of the ship around 32°. Toilets and showers unusable. Bad and expensive restaurant (see here).
3. The Saint Gotthard tunnel (Switzerland): systematic tailback (three hours). Use the pass instead, between Airolo and Göschenen.