Banja Luka's Kastel Fortress by the Vrbas River, aerial of cityscape, Bosnia

banja luka kastel fortress vrbas river aerial historical park urban greenery city bosnia herzegovina fortress walls landmark nature trees fort riverbank eastern europe architecture stone cultural scenic cityscape landscape medieval balkan public garden summer outdoors panoramic sightseeing tourist spot clear water daytime sky recreation walking paths heritage traditional community leisure old riverside defense iconic travel destination balkan peninsula local attraction historical structure