Alte Burg Penzlin, Medieval castle in Penzlin, Germany.

Alte Burg Penzlin is a castle founded around 1220 in Penzlin, southwest of Neubrandenburg. It served as a secondary residence for the Princes of Werle and later became the ancestral seat of the von Maltzahn family. The castle includes a cellar known as the "Hexenkeller" (witch's cellar), installed from 1560, and a courtyard herb garden with plants credited with magical powers.

The fortress was founded around 1220 as a seat for the Princes of Werle and later passed to the von Maltzahn family. It was damaged during the Thirty Years War, and those scars remain visible in the building today.

The castle's name echoes the medieval border post Isern Purt (Eiserne Pforte) that stood in the Penzlin area in the 12th century. Since 1990 a local knightly association, the Wächter der Isern Purt, has organised an annual medieval castle festival with jousting and re-enactments of knightly life in the Penzlin region.

The castle courtyard and exterior can be viewed without a guide, but the interior rooms and the Hexenkeller are accessible only with a museum ticket. The site was extensively restored from 1990 onward. The museum also runs activities for school classes and holiday groups, listed on its website.

The museum holds a remarkable collection about witch prosecutions in the region with documents and artifacts from several centuries. This exhibition reveals how fear and legal systems worked together to accuse and judge people in past times.