A crowd spills along the sidewalk outside Proces, Belgrade’s boisterously intimate natural wine bar in historic Stari Grad. In this corner of the Old Town, the energy is decidedly new: a soft neon glow rings the room, where a DJ bumps bass-heavy electro while 20- and 30-somethings sip Serbian orange wine and light up cigarettes around high-tops. (Smoking indoors is still legal by exception in bars and restaurants here.) Outside, I catch strands of Serbian, Russian, English, and French as I thread through the crowd in search of Katja, a new friend I’d been introduced to earlier in the week.

“It’s our little wine circus, where anything can happen on any given night,” says Ekaterina Sumenkova, or Katja, who co-owns the bar with her partner, Griša. This seems an apt description of Belgrade in general: The city thrums with a dynamic energy that seems poised to shape-shift, to carry you from kitschy speakeasy to rowdy street party, or homey kafana to hip wine bar, at a moment’s notice.

A park in Serbia.…