North of Pregrada, in the Kunagora system, there is the Kostelgrad fortress, above the curve of the Kosteljina River. It is located on the top of a hill overgrown with deciduous forest on a rock at the elevation of 427 m, and was built to defend the Sutinsko passage on the Kosteljina River. It was the entrance to the Kingdom of Slavonia from the northwest and had great strategic importance on the border with the German Empire, guarding its western border. It was built in the 13th century and flourished during the Keglević family.
The fortress is a favorite picnic spot with a beautiful view of the northern walls on Bregi Kostelski and Donačka gora in Slovenia. But the most special feature is the beautiful southern view of the Sutinska valley, a narrow gap along the Kosteljina River through which you can enter the town of Pregrada from the north. The access to the fortress is easy and is accessible from its northern side from the settlement of Kostel, whereas the other sides are naturally protected by the steep slopes of the hill.