A recurring imaginative and pseudohistorical tradition centred on lost lands, vanished continents, and civilisations believed or imagined to have been destroyed by flood, geological catastrophe, or submergence. 

Its best-known example is Atlantis, first described by Plato, but related traditions include Lemuria, Mu, and Hyperborea, which were variously developed through nineteenth-century pseudoscience, Theosophy and occult discourse, pseudoarchaeology, pulp fiction, fantasy, and science fiction. 

Over time, the Drowned World shifted from supposed ancient geography to a more flexible cultural trope: a way of imagining lost civilisations, submerged histories, environmental catastrophe, and even the future disappearance of our own world.