Schloss Zwentendorf, Heritage castle in Zwentendorf an der Donau, Austria.

Schloss Zwentendorf is a three-part late-Baroque castle complex on the south bank of the Danube, about 215 metres from the river. Its two-storey manor house has a high hipped roof of red and black tiles, seven-axis sides with corner risalits, and a north facade flanked by two square corner turrets with metal-covered hoods and open lanterns. A column-supported veranda projects from the south side, and an 18th-century economic courtyard and a late-19th-century neo-Baroque dwelling complete the ensemble.

A medieval estate at Zwentendorf passed by purchase to Baron Christoph von Althan in 1595. After Gundaker Ludwig Josef von Althan died in 1747, his heirs built a late-Baroque country palace around 1750 as a second residence. When Schloss Goldburg burned in 1809, the counts moved their main seat here in the early 19th century, transferring usable decorations; late 19th-century work gave the present form.

The castle is also known as Schloss Althann, after the family that still owns it and runs a Demeter farm in the 18th-century economic wings. The baroque putti on the pillars at the passages beside the manor house came from Schloss Goldburg, the family's burnt-out ancestral seat, and were moved here when the castle was rebuilt.

The castle stands on the southern bank of the Danube, about 215 metres from the river, in the market town of Zwentendorf an der Donau. It is privately owned and cannot be visited; the grounds and buildings are only visible from outside. The baroque central axis of the park runs north from the manor house to a wrought-iron gate and continues as a clearing toward the Danube.

The baroque garden's central axis survives as a visible clearing in the greenery: it runs from the manor house north through a lancet fence gate flanked by early 18th-century columns with vase finials, brought here from the burned Schloss Goldburg, and continues across the Danube to the Eleonorenhain hunting lodge over 2.5 km away.