Schloss Karlau, former building in Styria, Austria

Schloss Karlau is a former hunting and pleasure palace built from 1584 to 1590 for Archduke Karl II. Its old wing has four storeys under a steep hipped roof, and the corner turrets with flat tent roofs once carried onion domes. Inside is a chapel dedicated to Saint Thomas, redesigned between 1967 and 1969. The palace now forms the core of the Graz-Karlau prison, so little of the original building is visible.

The castle was built between 1584 and 1590 by Italian and Swiss architects for Erzherzog Karl II. After Karl's death, his widow Maria expanded the palace, and the building later served various purposes from a prisoner facility in the 1700s to a modern penitentiary.

The castle was once the heart of a large hunting estate, and nearby street names still recall this history. The chapel dedicated to Saint Thomas inside shows the site served religious purposes for the ruling family beyond its role as a hunting retreat.

The castle sits in southern Graz in the Gries district and is viewable from outside the street, though the interior is not open to visitors. The surrounding streets and parks offer good insight into the historical importance of the site.

The name Karlau comes from the marshy floodplain, the Au, that was named after Archduke Karl II. The palace was nearly called Schloss Dobel, but that was dropped to avoid confusion with the hunting lodge Tobel near the village of Dobel southeast of Graz. The moat-like ring wall had four towers, among them the Spitalturm, partly demolished in 1714, and the Hundsturm.