Duke's Chest Castle, Gothic castle in Ingolstadt, Germany.

Duke's Chest Castle, also called Altes Schloss, is a Gothic secular building begun around 1255 in Ingolstadt. It rises eight storeys, built of rubble and brick, with stepped gables divided by pilasters on the end walls and a small oriel on the west side marking the former castle chapel. A round town-wall tower from the 13th century adjoins the east side.

Duke's Chest Castle was built around 1255 on the orders of Louis the Strict as a palas (residential building) of the Ingolstadt residence, making it the oldest surviving non-ecclesiastical building in the city. It was originally part of a larger complex of outbuildings around a courtyard. It served as the ducal residence until the New Castle was completed in the 15th century, and was probably converted into a granary only at the end of the 17th century.

The building's name, Herzogskasten ("duke's chest"), recalls its later use as a ducal granary, unlike the smaller namesake buildings in Abensberg and Kelheim. Since 1981 it has housed the Marieluise-Fleißer-Bücherei, the city library named after the Ingolstadt writer Marieluise Fleißer, and the Stadttheater runs a studio here.

The building stands in Ingolstadt's old town, near the first rectangular city wall that bordered the Schutter to the south. Since 1981 it has housed the Marieluise-Fleißer-Bücherei, the city library, open to the public since its 1974 renovation. The Stadttheater Ingolstadt also runs a studio inside. Visitors enter through the library, whose 1978–1980 conversion by architects Branca, Brand and Falkner added concrete coffered ceilings and wooden galleries.

The fortress was built not merely as a military stronghold but also served as a residence for the ducal family and their court. This dual purpose made it a center of power and culture in the region.