Hrvatska Kostajnica, a long-standing and proud Croatian city whose position has determined its role, is located along the banks of the Una River and is located in Sisak-Moslavina County. The old town of Zrinski is a fortress from the 13th century, which during the wars with the Turks won the title of Defender of Croatia.
In the second half of the 13th century, the princes of Kostajnički established their center on the Una coast. Most of the information about the construction of the fort dates from the 14th and 15th centuries. The fortress was of great importance to the Zrinskis because it provided them with defense. The name Zrinski grad is reminiscent of the Siget hero Nikola IV. Zrinski.