Pant y Meddygon (the Dingle of the Physicians) features in the famous local legend of the Physicians of Myddfai (though curiously the stones aren’t mentioned. Perhaps the stones now represent the physicians?). The Otherworldly Lady of the Lake used to visit her sons here, showing them the plants and explaining their medicinal properties.
You can read the whole story at the Sacred Texts Archive
sacred-texts.com/neu/cfwm/cf105.htm
where it is part of John Rhys’s ‘Celtic Folklore, Welsh and Manx’ (1901). He was quoting a writer from 1860 who had based his writing on local accounts.