The Abbey can be visited
St.-Johannis Church

The St.-Johannis Monastery in Schleswig, situated on the northern bank of the Schlei, is the best-preserved medieval monastery complex in Schleswig-Holstein. Originally founded as a Benedictine nunnery, it transformed into a convent for noblewomen after the Reformation, yet retained its historic name and architectural integrity.
History+
The St.-Johannis Monastery was founded in 1194 on the Holm, an island in the Schlei near a fishing settlement outside Schleswig. It was dedicated to Saint John the Baptist. An earlier Benedictine settlement in Schleswig, St. Michaelis Monastery, was dissolved in 1192, though the exact connection to St. Johannis is not clearly historically proven. In 1251, Danish King Abel confirmed extensive freedoms for the monastery. By the end of the 14th century, it was explicitly referred to as a Benedictine nunnery. Fires in 1299 and 1487 led to destruction and subsequent rebuilding.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Kloster_St.Johannis_Schleswig.JPG
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 54.5116, 9.5789