Several Arsène Lupin novels contain some fantasy elements: a radioactive 'god-stone' that cures people and causes mutations is the object of an epic battle in "L’Île aux trente cercueils"; the secret of the Fountain of Youth, a mineral water source hidden beneath a lake in the Auvergne, is the goal sought by the protagonists in "La Demoiselle aux yeux verts"; finally, in "La Comtesse de Cagliostro", Lupin's arch-enemy and lover is none other than Joséphine Balsamo, the alleged granddaughter of Cagliostro himself.