The most popular place in my country has to be the Cox's Bazar and it is popular worldwide. I have been there several times and I will go there again several times in the future. It is an awesome place.
Bali is a tour site that's very popular among the international traveler. I'm sure you've at least once heard about the beautiful beaches on Bali because how popular Bali is (sometimes even more popular than Indonesia itself).
There are more such places, but perhaps I would single out the Kalemegdan fortress in Belgrade, as well as the Petrovaradin fortress in Novi Sad. And there is also the archaeological site 'Lepenski Vir'.