The remains of the Castle can be visited
Drachenfels Castle

The Drachenfels Castle Ruin, a landmark in the Siebengebirge mountains, is near Königswinter in North Rhine-Westphalia. As the remains of a hilltop castle, it offers a view over the Rhine Valley.
History+
The origins of Drachenfels Castle date back to 1138, when Archbishop Arnold I of Cologne began its construction. Ten years later, in 1149, Gerhard von Are, the provost of the St. Cassius Abbey in Bonn, acquired the unfinished complex and completed it. Its strategic location at the beginning of the Cologne Bay. By 1634, the castle was already damaged and was no longer repaired. Just four years later, in 1638, Protestant Swedish troops captured Drachenfels and razed its outer defenses. The trachyte quarries, which supplied building material for Cologne Cathedral, moved closer and closer to the mountaintop.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.zeche.org/
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Location: 50.6652, 7.2101