The remains of the Castle can be visited
Kaster Castle (Ruin) (Kaster)

The Kaster Ruin, a remnant of a castle complex, rises on a small hill in the Rhein-Erft-Kreis in North Rhine-Westphalia. Located at an Erft crossing and a trade route, it shows the territorial rivalry between the Archbishops of Cologne and the Lords of Jülich.
History+
The origins of Kaster Castle date back to 1148, when it was owned by a nobleman named Heinrich von Caster. In the 13th century, the complex passed into the possession of the Counts of Jülich, who expanded it into a seat for a collateral line of their house. The visible remains today mainly stem from a new construction in 1278. Between 1328 and 1337, the castle served as the dower seat for Elisabeth of Brabant.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 51.0113, 6.5567