Fortress Kostajnica

Kostajnica Fortress occupies an islet in the Una River, immediately beside the border with Bosnia and Herzegovina. Documents mention it as a fortress in the early 15th century, and its history was marked by changing owners and defence against the Ottoman Empire. The Zrinski family took possession in 1528 and strengthened it, but the Ottomans captured it in 1556 and held it until 1687. Research has identified six building phases: the key feature is the square keep, joined by a west-facing pentagonal tower and a later round artillery tower. After the 1990s war, the fortress was formally returned to Croatia in 2002 and conservation work resumed.