The walled Ottoman core of Trebinje, enclosed by a hexagon of 18th-century stone walls and entered through one of two gates. Inside, the streets are narrow and stone-paved; the central Osman-paša Resulbegović Mosque dates from the 17th century but the surrounding buildings are mostly Austro-Hungarian from the late 1800s, with shuttered windows and modest stucco facades.
The old town is now packed with cafes, small bars, and a few craft shops, and is genuinely lived in — not a museum. Allow an hour to walk it slowly. At dusk, locals begin the korzo, the evening promenade up and down the plane-tree-lined Slavoluk pobjede (Victory Square) just outside the walls. Free; the mosque is open during prayer times.