Ribnik Castle - Stari grad Ribnik, Ribnik, Karlovac County, Republic of Croatia.
The Rybnik castle is one of the few remaining medieval lowland forts. Its defensive structure is of particular interest: in case of danger, residents could dam a nearby stream and flood the surrounding area, thus turning the fortress into a fortified island.
The fortress was built in the 14th century during the Frankopan family's reign. Since the late 16th century, the fortification has belonged to the Zrinski family, and subsequently, through several other owners, the castle has served various purposes. It housed a school, a post office, and even a warehouse.
The fortification is two-story and accessible by a drawbridge. Its base is irregularly circular, with an inner courtyard, and the eastern defensive tower still bears the Frankopan family coat of arms. Numerous Gothic and Renaissance details, such as windows and doorframes, have also been preserved.