Frankopan Castle, Medieval stone castle in Ogulin, Croatia

Frankopan Castle is a Renaissance water castle in the centre of Ogulin, built on an irregular quadrilateral plan next to the Đulin ponor, the sinkhole where the Dobra disappears. It was erected by Bernardin Frankopan at the end of the 15th century and is locally called Stari grad (Old Town). A castle chapel dedicated to Saint Peter was built during construction.

The Frankopan noble family built this fortress around 1500 as part of their network of castles across Croatian lands. The structure served as a key defensive position for the region over subsequent centuries.

The castle houses a regional museum with collections of traditional weapons, furniture, and documents from the Ogulin area. Visitors can explore how local people lived and worked through the displayed objects and everyday items.

The castle stands in the centre of Ogulin, right beside the Đulin ponor sinkhole where the Dobra disappears underground. Locals call it Stari grad (Old Town). The regional museum has occupied the building since 1967, so visiting means walking through its collections rather than ruined halls.

The castle stands beside Đulin ponor, the sinkhole where the Dobra disappears into the ground in central Ogulin. The fortress was built next to this pit, and the town grew around both. The museum inside holds a memorial room for Ivana Brlić-Mažuranić, the Ogulin-born writer, alongside archaeological, ethnographic and old-weapons collections.