Surely not even the two mysterious gentlemen themselves would have ever suspected that their stay here would last more than thirty years when they arrived in Hildburghausen on February 7, 1807. That evening, an elegantly dressed couple checked into the English Court Hotel and, from then on, attracted attention with their strange hermit lifestyle. This very conspicuously secluded lifestyle intensified after they moved to the castle in the neighboring village of Einhausen. Above all, no one saw the always-veiled lady. She died in the solitude of Einhausen Castle on November 25, 1837, and was buried—according to her wishes—on Hildburghausen's town hill. Source: thueringen.info/grab-der-dunkelgraefin.htm
If you follow the link, you will see that incorrect images are mistakenly declared as graves. The actual grave (not a cellar hole) is further up and you have to follow the path for another 100 meters.