Knez Mihailova is the main walking street in the center of Belgrade. It goes from Kalemegdan (central park and fortress) to the Repubic Square (main central square), and continues to Terazije square, splitting the downtown in two. This street is one of the best places to feel the pulse of the city.
https://www.tob.rs/en/what-to-see/belgrade-attractions/knez-mihailova