Kalemegdan park

Kalemegdan is Belgrade’s central park and fortress complex lying on a hill overlooking the Sava and Danube confluence, on the eastern side of the river Sava. This has been the sight of the ancient Roman city of Singidunum, the medieval and Turkish era Belgrade and was converted into a park in the mid 19th century. It is home to several galleries and museums, restaurants, sports courts, and the Belgrade Zoo.
Besides many kilometers of paths and numerous hideouts through the park, there’s also a few playgrounds for the kids, some chess boards from the elderly, and a great wall which is a favorite spot for teens & youth with spectacular and often romantic views of sunsets, storms or other beauties of nature. In winter, the younger population goes skiing and sleigh riding on the slopes near the Zoo, or ice-skating at the court near the Sahat (Clock) tower.
The park is also home to squirrels and other smaller animals which from time to time like to hang around with people, specially if you have some food to offer them.
If you don’t like walking, you can also get the mini train that runs through the park.