The remains of the Castle can be visited
Sokolac Castle

In the small town of Brinje, the castle ruin of Sokolac stands, an example of Gothic architecture in Croatia. It houses the best-preserved castle chapel in the country, dedicated to St. Mary.
History+
The first documented mention of Sokolac Castle dates back to 1411. It was owned by the noble Frankopan family and was built by Nikola IV Frankopan as a new center of power for his family. Ivan Anž VI Frankopan Brinjski was the first Frankopan to reside there. Adjacent to the castle, a fortified settlement was established, forming an irregular hexagon protected by four semicircular towers and a bastion. In the parish church of St.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Sokolac_Brinje_07_2.jpg?uselang=de
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 44.9983, 15.1318