If you come to Serbia, I highly recommend visiting the two places.

1. Novi Sad. It takes only half an hour to get there by train. It is a very comfortable city with a slow pace. It is fun to feed pigeons n the square and eat ice cream.
2. Zemun town. The beautiful Danube River and lovely swans. If you like, it is great to feed the swans. Or it is also very comfortable to sit by the lake, drink a cup of coffee, and spend an afternoon.