The historic centre of Belgrade is known in the Serbian language as "Stari Grad" (old town). There are plenty of interesting places to explore: the ancient Roman Cardo, the current pedestrian street Knez Mihailova with its commercial shops, the Kalemegdan Fortress and the Republic Square. Another central plaza is Terazije, near the charming pedestrian street of Skadarlija. You can also visit the nearby fruit and vegetable market.
May 25 was the date of birth of Tito, and on that day, since 1945, World Youth Day has taken place. Its a relay race with the best students from each country of Yugoslavia who have to arrive in Belgrade and hand the baton to the Mariscal. In the museum, which also houses the tomb of Tito in a building known as the "House of Flowers", that recalls the past glories is preserved, including a giant photograph of the leader of the No Passing Aligned Movement, the political movement created by Tito. You can get on bus 41 from Student's square, or walk.
There are lots of fun activities, bars, a beach, an adventure park... But it can get very crowded on a hot day. In the winter, it's nice to walk and explore different routes around the lake, it's still very pretty but it's kind of empty and not as much fun.
If you get the chance you have to take a walk across the bridge. The view of the confluence of Sava and Danube, the fortress Kalemegdan and other parts of Belgrade is absolutely stunning.