The Castle can be visited
Löwenburg Castle (Kassel)

Löwenburg Castle in Kassel is an edifice, not built as a medieval fortress but deliberately constructed as an artificial ruin in the Neo-Gothic style. It is situated in the southern part of the Wilhelmshöhe Mountain Park and is an early example of Neo-Gothic architecture in Germany.
History+
Construction of Löwenburg Castle began in 1793 under Landgrave Wilhelm IX of Hesse-Kassel, who used it as a private retreat. The designs were by Heinrich Christoph Jussow, and the construction lasted until 1801. Initially, only a ruined tower was planned, but it evolved into a complete castle complex surrounding an inner courtyard.
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: 51.3114, 9.4086