Haus Altenburg, Medieval castle in Gangelt, Germany

Haus Altenburg is a former knight's estate in the Saeffelbach valley near Breberen, built on the site of an early motte of the lords of Heinsberg. It consists of a three-sided, two-storey outer bailey of the 17th and 18th centuries and a three-winged manor house reached by a rising brick bridge. All buildings are of brick and are partly surrounded by moats.

Haus Altenburg was built by the lords of Heinsberg on the site of an early motte-and-bailey castle and was first documented in 1330 as "Hof ten berghe". The three-winged manor house took its present form in 1782, while the gatehouse and side wings date from the 17th and 18th centuries. The estate remains in the possession of the Counts von und zu Hoensbroech.

The name Altenburg alternates in the records with Alteburg and the older Haus Breberen, after the village beside it. The estate remains the property of the family Graf von und zu Hoensbroech, whose double coat of arms with that of the Bocholtz appears on the house portal and inside the west wing, dated 1628.

Haus Altenburg lies in the Saeffelbach valley just outside Breberen, a district of Gangelt. It is a private estate still owned by the family Graf von und zu Hoensbroech, so the grounds and buildings are not open to visitors; the brick bridge, gate and outer courtyard are best viewed from the public approach road.

The cellars of the manor house contain a late Gothic pillar, probably reused from an earlier building on the site. The gate of the outer bailey also carries a coat-of-arms stone dated 1714 with the arms of the von Blanckart family.