Burgruine Zeiselberg, Medieval castle ruin in Magdalensberg, Austria.

Burgruine Zeiselberg is a castle ruin in Magdalensberg featuring a rectangular residential tower positioned at the summit and sturdy wall segments on the northern and western faces. The fortification spans approximately 640 square meters and retains substantial remains of its original medieval construction.

The castle was built around 1250 by Albert, son of Hainricus Ziesel, as a fortified stronghold in the region. Destruction came in May 1293, after which the castle was never rebuilt.

The village of Čilberk, the only settlement in its cadastral municipality, grew out of the medieval castle and takes its name from it. The local Slovene dialect of the Klagenfurt plain, house names such as Kraut, Muhl, Tamiš and Habner, and field names like Zeiselberger Feld were recorded by the writer Bojan-Ilija Schnabl, a native of the area.

The ruin stands at 600 m above sea level on the hill above the village of Zeiselberg, in the municipality of Magdalensberg. The core of the castle is protected on the north and west by a deep neck ditch, and the gate in the east leads into the small inner courtyard. The original masonry is mostly preserved only up to knee height, while the bergfried has been rebuilt to a height of eight metres. A local association works on researching and using the ruin.

Excavations since 1989 have yielded horseshoes, belt buckles, crossbow bolts and an alembic, a distillation vessel. Because the castle stood only a few decades, these finds were not disturbed by later rebuilding and give an undisturbed picture of everyday life in the 13th century.