If this is the Kallenberg Castle in Baden I have a few photos I can send. They are pictures of the remnants of the castle after it was burned in the late 1800s I believe. This would have been somewhere in the time period of Ernest11 - the Duke of Saxe - Cobourg - Gotha - His father had gifted the castle to the duke shortly after his marriage to Princess Alexandria of Baden - *I would love to
see a photo of the painting if that would be possible!
Thank you, and I hope this information helps you in some way