Belgrade Fortress

The Belgrade Fortress, consists of the old citadel and Kalemegdan Park on the confluence of the Sava and Danube rivers, in an urban area of modern Belgrade, Serbia. It is located in Belgrade's municipality of Stari Grad. Belgrade Fortress was declared a Monument of Culture of Exceptional Importance in 1979, and is protected by the Republic of Serbia. It is the most visited tourist attraction in Belgrade, with Skadarlija being the second. Since the admission is free, it is estimated that the total number of visitors is over 2 million yearly.

Source: Wikipedia