Which balkan country would be the best to visit for culture and city travel?

Me and my dad want to go to the balkan this year. Specifically 1 country. Were going around june/july and we are probably going for 1/2 weeks. We dont know with which transport were going yet.

We both really want to go to some tourist areas and city hopping, but also going to some cultural spots or however u call them. I want to make sure that its traveable from one place to another.

Which country doesnt matter overal, but my dad doesnt feel like going to croatia, bosnia and serbia since he has been there a few times before. I personally dont mind

I genuinely dont know what else to add so if you have questions feel free to ask.

Thanks in advance!