+1 for Dubrovnik, I stayed in the little village of Cavtat (pronounced tsavtat) in May which is a cheap 30 bus ride up the coast from Dubrovnik. Or you can take the water taxi there and back if you prefer, it's a great way to arrive in the Medieval walled city. When you jump off the boat you are right in the city, unlike getting off at the bus stop which involves a 15 minute walk down to the old town walls itself.
Cavtat is nice, only a couple of beaches, low key nightlife - no nightclubs, plenty of bars, restaurants and cafes to go at though.
If you visit Dubrovnik I highly recommend taking the cable car up to the summit of Mount Srd, the views from the top are spectacular. Dubrovnik 700ft below you, Lokrum and Elafiti isles surrounding that (all of which you can visit by boat) and the Stunning Adriatic sea stretching out to the horizon. There are loads of Museums in Dub too if that's your thing.
We also booked an excursion to Mostar in Bosnia with its new Old Ottoman bridge (Destroyed by shelling in the 90's Bosnian War and restored in 2005 at a not insignificant sum of $10 million USD, no, war really does not make sense!) - a town where they are slowly regaining their trust in one another, Ethnic Muslims (Bosniaks), Serbs (Orthodox Christian) and Croats (Roman Catholic). Shocking scars of war still are in plain sight with shell damaged buildings dotted about everywhere and the thousands of graves in the town cemetery, most of which to the young men who were only in their 20s or late teens when they died. :( A very sobering place to visit but it makes you appreciate what you have. All the while the town is juxtaposed by having a stunning surrounding countryside. The tour guides are very informative and are not scared of telling you all about what went on in the war so don't be afraid to ask tactfully if you wish! Emotions and feelings are understandably still raw with many of the towns inhabitants though.
Shell damage is not too hard to spot in Dubrovnik too, almost hard to believe only 20 years ago it was being pointlessly shelled by the Serbian authorities of the time. A shocking criminal act on an innocent civilian town. Oh well, hope I haven't put you off after all that! Lol