Most of the legends surrounding Ciri state that the final battle between Geralt and Vilgefortz took place here. However, this was a ruse by the Lodge of Sorceresses to cover up the truth: they thought they'd gotten the upper hand in capturing Ciri to use her for their own political agenda but were instead outsmarted by the witcher, who gave them this location as Vilgefortz's hideout, when in actuality it was Stygga Castle. By the time the sorceresses learned the real location, they were too late as Ciri had reunited with her adoptive parents.
To prevent future generations from learning the truth, the Lodge utterly destroyed Stygga and let it pass into legend that Rhys-Rhun was the location. This appeared to work very well, as only one known story, The Black Book of Ellander, mentions Stygga as the real location of the final battle.