The movement pattern that works
Walk the center, ride the longer edges.
- Walk Kalemegdan, Knez Mihailova, Republic Square, and Dorcol.
- Use rides for Zemun, farther Vracar, or late returns.
Belgrade's center rewards walking because the city changes texture quickly: fortress, pedestrian street, side lanes, cafes, and old restaurants. But the city also spreads, and long jumps can drain the day.
I would build one zone first, then add a ride only when it helps. That keeps the city feeling generous rather than messy.