Burgruine Petersberg, Medieval castle ruins in Friesach, Austria.

Burgruine Petersberg is a ruined hilltop castle above Friesach, dominated by a six-storey bergfried built around 1200 that now houses the Friesach City Museum. Beside it are remains of an older chapel (Gebhards- or Konradskapelle), and the lower bailey preserves a 16th-century three-storey building with an arcaded courtyard front, now an inn. The upper bailey stretches to the rocky summit, flanked by a shell tower on its north and south sides.

Archbishop Adalwin of Salzburg received the estate in 860, and castle construction began around 1076 during the Investiture Controversy. The fortress became an important religious and administrative center of the region during this period.

The six-storey keep, built around 1200, now holds the Friesach City Museum, with exhibits on the town's history, culture, mining and trade. The tower also contains the monumental Rupert Chapel, and beside it stand the remains of the older Gebhard or Konrad Chapel.

The site is located on a hilltop, so sturdy footwear is recommended and the path can be steep. The castle and attached museum are open daily to visitors, but check specific opening times before planning your visit.

The Upper Courtyard, a walled area reaching the rocky summit of the Petersberg, is flanked on its north and south sides by one shell tower each — open-backed towers whose rear side was left unbuilt against the curtain wall. The main entrance lay to the west, north of the Upper Courtyard, where part of a former gate tower survives.