Montenegro is a pretty country, and if you visit just one place then you could do a lot worst than basing yourself around the Bay of Kotor on the Adriatic coast. Because of it's shape many people believe the bay is a Fjord, but it isn't. It is however very beautiful.
The city of Kotor is set deep in the bay and the old city, which is surrounded by thick stone walls is like a mini Dubrovnik - without all the tourists. It's small enough just to wander the streets and get lost, eventually you'll emerge into one of the squares and be able to reorientate yourself.
The walls that surround Kotor climb high into the hill behind the city, rather like a mini Great Wall of China, but during the day it's rather difficult to see as the rocks of the wall blend into the rocks of the hillside. At night however the wall is lit up, and it looks like a halo above the city.
The one thing to watch out for in Montenegro is the 'tourist season' if you visit outside this ill defined time you make have issues, as B&B's, car hire and other tourist related companies seem to go into hibernation. It seemed to me quite strange that the companies decide when the season starts and ends rather than wether there are tourists there or not.
Another gem around the Bay of Kotor is the village of Perast, a tiny little place that has great views of the bay, and two islands just off shore - one is called St. George island, and the other Our Lady of the Rock.
The bad news was that by the time I arrived all the boats over to the islands had stopped, I was bitterly disappointed. After walking around the waterfront for a bit I spotted a bloke in a small boat coming into shore. as he approached I gave him a wave and a 'hello'. After a bit of chat I found out that he was a photographer and lived on the other side of the bay. Soon after that I was in his boat and heading off to the Our Lady of the Rock!
It appears that both island are to an extent man made, as they started out as partially sub merged rocks that have been built up over the years.