Haus Demmin, Medieval castle ruin in Demmin, Germany

Haus Demmin is a castle ruin sitting on a small river island in the center of Demmin, where the Tollense and Peene rivers meet. Sections of the old fortification walls still stand, and the grounds show traces of both the inner fortress and an outer defensive enclosure.

The fortress was founded in 1127 as a stronghold for the Pomeranian rulers and served as the seat of the Pomerania-Demmin dynasty until the line ended with the death of Wartislaw III in 1264. During the Thirty Years War, fighting between Swedish and Imperial forces left the site heavily damaged, and the defensive tower was pulled down in 1648.

The remaining brick walls show a building style that was common in this part of Pomerania during the Middle Ages. Visitors can still make out how the site was divided into a main fortress area and a forward outer section.

The site lies on an island at the mouth of the Tollense, southeast of Demmin's old town, and can be reached on foot from the town centre. The grounds are unguarded open terrain; the brick stump of the defensive tower and the walls of the 19th-century manor stand in the open. Paths are unpaved, so wear sturdy shoes after rain.

The round brick keep, dated to around 1200, is the oldest surviving secular building in Pomerania. Its ground plan was originally octagonal and star-shaped, a form also used at Castel del Monte in Sicily. The visible walls include many later repairs, and the 2008 consolidation was criticized by conservationists.