entrance of saint petka's chapel located in belgrade fortress or beogradska tvrdjava kalemegdan park on the confluence of the riv

archeological architecture balkan battlefield belgrade beograd beogradska building capital caste castle chapel city danube destination europe fort fortification fortified fortress gate green hill historic historical history kalemegdan landmark leaf medieval nature nobody observation outdoor park petka river saint serbia serbian sightseeing stone stream stronghold tourism tower tvrdjava wall walls