The remains of the Castle can be visited
Hardtburg Castle

The Hardtburg, a water castle ruin from the High Middle Ages, is situated on the northern edge of the Eifel near Euskirchen's Stotzheim district. Although parts of the core castle have been in ruins since the 18th century, the extensive castle walls and the outer bailey are well preserved.
History+
The origins of Hardtburg likely date back to the 11th or 12th century, with a Lord of Har(d)t considered a possible builder, documented from 1105. Its first written mention appears in 1166. In 1205, Archbishop Bruno von Sayn captured and partially destroyed the castle.
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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: 50.6142, 6.8139