Zvornik Fortress, Medieval fortress in Zvornik, Bosnia and Herzegovina

Zvornik Fortress, also called Kula Grad, is a medieval castle on the Mlađevac mountain above Zvornik, made up of three linked parts: the Lower Town beside the Zvornik–Sarajevo road, the Middle Town with the 20-metre White Tower, and the Upper Town at about 407 metres above sea level, overlooking the Drina and Zvornik Lake.

The fortress was founded in the late 13th century and then passed through the hands of Bosnian, Hungarian, Serbian, and Ottoman rulers. These repeated changes of control left their mark on the architecture and structures visible today.

Locals call the fortress Kula Grad, "Tower City", after the three towers of the Middle Town, the largest being the 20-metre White Tower. Legend credits its building to Prokleta Jerina, the wife of Despot Đurađ Branković, and says slaves passed stone blocks hand to hand from a quarry 12 kilometres away. The tunnel under the Lower Town wall is still called the Town Gate.

Visitors can reach the fortress on foot via a path of about 1700 meters from the town center or by vehicle along a road of about 7 kilometers. The choice of route affects how much time the journey takes.

The Large Tower in the Middle Town section stands about 20 meters tall and displays building styles from different eras across its walls. This tower is a particularly good example of how different rulers left their marks on the place.