The Graukloster — the Grey Friars' monastery — was founded in the 13th century by Franciscans and is one of the best-preserved medieval monastic complexes in Schleswig-Holstein. The name comes from the grey habits the Franciscan friars wore. After the Reformation, the buildings passed through several uses before eventually finding their current role as a retirement home, which means they remain in active use rather than standing as a ruin or museum.
The Gothic cloister and the late-medieval church are the architectural highlights. The complex is not always open to the public, but the exterior and the church can often be visited. It lies a short walk east of the Dom, tucked into a quiet corner of the old town.