Burgruine Grafenstein, Medieval castle ruins in Grafenstein, Austria.

Burgruine Grafenstein, also called Altgrafenstein or Lerchenau, is a ruined hilltop castle on a roughly 20-metre rock cone on the northern slope of the Skarbin, south of Grafenstein. Only the north side is accessible. Traces of masonry and the Romanesque ground plan remain, along with natural caves and niches in the rock that were evidently enlarged and show remnants of walls.

Burg Altgrafenstein was first documented on 20 June 1158, when Bishop Roman I of Gurk enfeoffed Duke Henry V of Carinthia with the estate and court of Gravindorf, the charter naming the castle as castrum gravenstaine. Lacking strategic value, Henry installed ministerials, beginning with Heinrich von Truchsen, whose sons Gottfried and Adalbert followed as burgraves. The castle passed to Hans Liebenberg in 1330 and to the Kraiger family in 1351; after the great earthquake of 1348 it appears in charters only as a ruined castle site (Burgstall). In 1629 Johann Andreas von Rosenberg acquired the lordship with the ruin, which faded into legend as the fictitious Schloss Lerchenau.

The castle gave its name to the Grafenstein family, whose seal — a griffin or wolf rising from a five-pointed crown — became the municipal coat of arms in 1954. After the ruin faded from records it passed into legend as the fictitious Schloss Lerchenau.

The ruin is reached via the Skarbin-Güterweg and can only be climbed from the north. The steep rock cone rises about 20 metres; the ring wall excavated by Franz Xaver Kohla in the 1920s is overgrown and buried again.

The castle is also called Burg Lerchenau, a name that grew out of legend after the ruin faded from records; the small Grafenstein castle became the legendary Schloss Lerchenau. The Grafenstein family took its name from this stronghold, and Rudolf von Grafenstein's seal, showing a griffin or wolf rising from a five-pointed crown, became the municipal coat of arms in 1954.