The Southern Gloom or simply Gloom, referred to mythical regions of Haradron tale and legend. Said to lie beyond the Southern coasts they may have referred to the Fiery Mountains, Home of Night, Nether Darkness and Nether Heats, the Island of Ungolianth, lands out of even older legend, the voyages of the Númenóreans or earlier Eärendil the Mariner.
It remains unknown if these lands were part of Southerness or maybe even less known islands between the Uttermost South of Middle-earth and the Southern Cold
see:
Editorial Note: This entry contains speculative or fan-based material — such as fanon, fanfiction, or theory constructs — that may not be directly supported by canonical texts. Interpretations offered here are part of the NNCA’s speculative corpus and should not be mistaken for primary Tolkien sources.