The mysteries of Mount Sibyl and the Lakes of Pilate, in the Sibillini Mountain Range in Italy, are both ancient enigmas which are still unsolved. In two previous papers, “Birth of a Sibyl: the medieval connection” and “A legend for a Roman prefect: the Lakes of Pontius Pilate”, we identified the presence of two additional, extraneous legendary layers, which are connected to the figure of Morgan le Fay and to the ancient lore concerning the burial places of Pontius Pilate. With a third paper, “Sibillini Mountain Range: the legend before the legends”, we pinpointed a number of common traits that mark both legends, the Cave's and Lake's, with at least three shared features: a legendary demonic presence; the performance of necromantic rituals; winds, tempests, and devastation which mythically arise from both sites. With the present paper we address a fourth, most significant feature which seems to mark the two sites, the Sibyl's Cave and the Lake of Pilate: they both appear to have been considered as some sort of passageways to the Otherworld, owing to the presence of specific narrative elements, such as the test bridge, that are usually found in literary works that depict visionary travels to otherwordly regions. The Otherworld and its accessibility to living men has always been an illustrious, emotional literary topic in the literary production of the Western tradition, since classical antiquity, through the advent of Christianity and across the centuries of the Middle Ages. From Homer's “Odyssey” to Vergil's “Aeneid”, from Pope St. Gregory the Great to the visionary dreams originated in medieval Ireland, and up to the legend of the Purgatory of St. Patrick, men have always been dreaming about the afterlife, its shadows, its demons and its punishments. In the present work we retrace the main literary instances of the visionary narratives on the Otherworld in the Western culture. In addition to that, we highlight the strong literary links which can be retrieved between the legendary tales of the Sibyl's Cave and the Lake of Pilate, in the Sibillini Mountain Range, and two most famous and successful narratives which depict two specific journeys to otherwordly regions: the legend of the Cumaean Sibyl, with the Lake of Avernus and the gloomy cave providing an access to the realm of the dead, and the legend of St. Patrick's Purgatory, featuring another lake, Lough Derg, and another sinister cave. In the present paper we show the recurrent contaminations of narrative themes that link the three different, and substantially unrelated, legends, in the form of a visible transfer of narrative topics and situations from the illustrious and widely-known Cumaean and Irish tales, to an Italian tale which appear to features some narrative and geographical traits in common, though set in a different setting and despite its total independence from the legendary narratives of Lough Derg and Cumae. A contamination that has travelled across the centuries of the Middle Ages, through the invisible streams of oral tales and storytelling, finally materialised within the fifteenth-century works written by Antoine de la Sale and Andrea da Barberino. The resulting, far-reaching assumption which arises from the present research work is that a legendary passageway to some sort of Otherworld might have been possibly situated, by an antique tradition that left some faint traces in the known literature, among the peaks of the central Apennines. And the landmarks for this mythical entryway would be associated, just like in Cumae and Lough Derg, to the same kind of landforms, a lake and a cave: they both would mark a sort of legendary 'hot spot' on the surface of Earth, where the mythical passageway would be located. In this framework, a number of questions are left open in the present paper: why should this Apennine site have been considered as a further entryway to the Otherworld? If our assumption is true, what sort of Otherworld was this? What sort of dreadful dream did men conceive by the Lake and Cave set in the mountains of the Apennines, in central Italy? What legend did live in this area before the medieval legendary tales about a Sibyl and Pontius Pilate settled themselves here? The highlighting of the otherwordly character marking the Sibillini Mountain Range, in Italy, may lead to an improved comprehension of the mythical nucleus of the legendary setting that inhabits those imposing mountains of Italy, opening a new path that will be fully addressed in a future, and conclusive, research paper, now under preparation. This article is Part 2 of the full paper on the above topic, and also part of an extended series of papers on the true origin of the Apennine Sibyl's and Pilatus Lakes' legends, a series that will include further papers that are about to provide additional, previously-unpublished information on the whole fascinating topic.