Kartause Marienburg, Medieval monastery near Dülmen, Germany.

Kartause Marienburg is a former Carthusian monastery in the Weddern hamlet near Dülmen, North Rhine-Westphalia. Its four-winged cloister was built inside the moat of the old Wasserburg Weddern, and the former monastery church of St. James, begun in 1477 and vaulted between 1487 and 1510, still stands. The gatehouse of the castle survives in altered form.

Gerhard von Keppel, hereditary marshal of Cleves, founded the monastery on 31 August 1476 in memory of his son, killed at the siege of Neuss in 1475. Three monks from Wesel moved into Weddern Castle in February 1477, and the first stone of the church was laid on 21 May. The house was incorporated into the Carthusian order in 1480 and dissolved in 1804 by the Duke of Croÿ with papal permission.

The monastery now operates as Anna-Katharinenstift Karthaus, providing residential spaces and workshops for people with disabilities. This active use shapes daily life at the site and demonstrates how a historic religious space serves contemporary needs.

The site is accessible for exploration of the preserved medieval structures and grounds. It is helpful to check in advance which areas are open to visitors, as the complex operates as a residential foundation today.

The gatehouse of the former Weddern water castle was reused for the charterhouse and survives in altered form. The monastic cloister, a four-winged layout typical of the Carthusian order, enclosed the old castle courtyard and its moat, so the defensive waterworks remained inside the monastery.