Perched on a hill above the emerald waters of the Una River, the Krupa Fortress is more than a ruin; it is a stone chronicle of empires, a silent witness to the ebb and flow of conquest and resilience in Bosnia and Herzegovina. Known also as Stari grad Pset, its fractured walls command a landscape that has been a contested border for a millennium, offering not just panoramic views, but a vista into a turbulent past.

The fortress first rose in the 13th century, a key defensive bulwark in central Pounje. Initially held by Croatian nobility before passing to the king, its very location marked a frontier. Its early history is tied to the parish of Pset, a name that still clings to the old stones. But it was the name "Krupa," emerging in that same century, that would endure, perhaps inspired by the local legend of a girl named Krupana who, spurned in love, built the fortress before casting herself into the river below.

The fortress’s medieval mettle was forged in fire against the expanding Ottoman Empire. In a display of defiant strength, its defenders repelled a siege by 2,000 Ottomans in 1509 and withstood a grueling four-month siege in 1522-1523. Yet, on June 23, 1565, the stone finally yielded. After a 20-day siege, a tiny garrison of 28 men led by Matija Bakić was overwhelmed by the forces of Mustafa Pasha Sokolović. This was not the end of the fortress's story, but a new chapter. The Ottomans, recognizing its strategic value for their westward ambitions, expanded and strengthened it, turning it into a formidable stronghold with a large, well-armed garrison. It proved its new masters' engineering, successfully resisting Austrian attacks in 1581, 1692, and 1716, and was recorded as still being well-supplied as late as 1833.

Today, the architecture tells this layered story in its very bones. The ruins reveal a formidable structure with one large and two minor round towers connected by bulwarks. Below, the outline of a fortified settlement with a wall, two artillery-adapted towers, and a gatehouse can still be traced. To walk along the remaining walls is to tread a path worn by Croatian knights, Ottoman janissaries, and Habsburg soldiers.

Now a major landmark, the fortress is a hub of cultural life, hosting music concerts and festivals that fill the ancient stones with new sound. It stands as the centerpiece of a remarkable tapestry of coexistence; within a small radius on the riverbank, one finds the fortress, a church, an Orthodox church, and a mosque—a unique testament to the region's complex cultural and historical layers.