The Castle can be visited
Scheffel Castle

On the Mettnau peninsula near Radolfzell am Bodensee, the Scheffelschlösschen stands as a structure in the Konstanz district. It is associated with the poet Joseph Victor von Scheffel and is distinguished by its Neo-Renaissance architecture.
History+
Joseph Victor von Scheffel regularly spent his summers with his family on the Mettnau peninsula starting in 1869. After being ennobled, he acquired the Mettnau estate in 1876 and had the existing vineyard tenant's house converted into a castle. He had already commissioned the construction of Villa Seehalde on Mettnau in 1872. The designs for the Scheffelschlösschen, in the Neo-Renaissance style, were created by Karl von Großheim, an architect from the Office for Architecture and Art Industry.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://schloesserrundschau.de/bawue/schloesser/konstanz14.html
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: 47.7278, 8.9956