Kostel Castle, Medieval castle on a hill above Kolpa River, Slovenia.

Kostel Castle is a fortified complex set on a hilltop overlooking the Kolpa River, featuring five towers positioned along its stone defensive walls. The layout includes multiple buildings and courtyards that once served different purposes and remain open to visitors today.

The castle was built between 1247 and 1325 by the Counts of Ortenburg and received its first written mention in 1336. It served as an administrative center and defensive stronghold for the surrounding territory throughout the medieval period.

The name Kostel derives from the Latin castrum, meaning fortress, and was first recorded in this form in 1449; the German name Grauenwarth was used for the castle itself. The settlement was also known as Trg (market town) after the Habsburgs granted it market rights. About a kilometre from the castle stand the gavge, a pillory-like structure that testifies to the castle's own court, which could pass death sentences.

The castle is best explored during daylight hours when the historic structures are most visible and the views of the surrounding landscape are clear. The site has pathways throughout, and comfortable shoes are recommended since the terrain has uneven surfaces.

The castle had its own court that could pass death sentences; the gallows (gavge) stood about a kilometre away and are cited in old records as proof of this judicial role. The settlement was also known as Trg ('market town') after the Habsburgs granted it market rights.