Fortress Kastel is a castle in Hrvatska Kostajnica, a town in central Croatia, near the border to Bosnia and Herzegovina. The fortress was built most probably in the 14th century and owned by the members of the noble families Frankopan, Lipovečki, Tot, Benvenjud and finally (in 16th century) Zrinski, so it is today also known as „Zrinski fortress“ or „Zrinski castle“ (). It was conquered by the Ottomans on 17 July 1556, but it was freed from their rule relatively fast, in 1688.