Schloss Harthausen, Royal palace in Rettenbach, Germany.

Schloss Harthausen is a double palace in Harthausen, part of the municipality of Rettenbach in the Günzburg district. The four-storey complex consists of two side wings from the 15th and 16th centuries, joined around 1760 by a four-storey connecting tract, with prominent curved gables. Arcaded remises to the west form the so-called Ehrenhof.

The site passed to Egolf von Riedheim in 1567, and the family still owns the palace. Its two side wings date from the 15th and 16th centuries. Around 1760, Baron Johann Alexander von Riedheim added a four-storey connecting wing and remodelled the whole complex in Baroque style, giving it its present form.

Above the gate, a stucco cartouche holds several coats of arms: the Riedheim arms in the centre, flanked by those of the Stauffenberg, Hornstein, Giel and Freyberg families, who were related to the Riedheims by marriage. The palace has belonged to the baronial Riedheim family since 1568.

Schloss Harthausen and its park are not open to the public; the complex belongs to the baronial Riedheim family and can only be viewed from outside. The arcaded remises west of the palace form the so-called Ehrenhof, beyond which lies the tree and grass garden documented since 1560. The former pleasure garden no longer exists.

About half of the palace windows are painted as trompe-l'oeil, creating an optical illusion on the facade. This clever painting technique was a fashionable way to demonstrate artistic skill and wealth at the time.