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"Ultraterrestrials" is a cross-genre book category for stories about intelligences and entities that are not simply aliens from other planets but beings that transcend ordinary terrestrial explanations — interdimensional visitors, ancient subterranean races, extradimensional predators, or consciousnesses that coexist with or invisibly shape human reality. These works blend elements of science fiction, horror, weird fiction, and paranormal investigation, emphasizing eerie unknowns, reality-warping encounters, conspiratorial cover-ups, and the unsettling idea that human history and perception may be influenced by nonhuman, often unfathomable intelligences. Narratives range from investigative thrillers and found-footage epics to atmospheric literary tales, but share a focus on the psychological and existential consequences of contact with entities whose motives, origins, and nature defy conventional science and mythology.

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