Few people believe that the dead find their final rest in places posited by long-defunct religions - fewer still pay Charon’s price - but sometimes they can be contacted.
Beyond the poetry of a belief in a transitional space between the world of the living and the afterlives of different faiths - a distance and separation that allows for journeys and quests that test and cross these same liminal borders - there is also a comfort in the idea that our world is not pressed up tight against the various realms of the nightmares and torments created to punish the unworthy and the unrepentant. The existence of other realties - some of which might function as paradises or purgatories and not the perditions entirely inimical to our immediate or existential wellbeing - is, broadly speaking, a given in the field, but tangible evidence for any specific cosmology tends to be tangential or indicative of the fringes of myths rather than absolute.
Maybe this is why, more often than not, any proof that can be found speaks to the connections between realities; the bridges and the boundaries. Such borders are, per legends, usually guarded or otherwise impassable, except through predetermined paths or under the protection of a guide set to that specific purpose. In Greek mythology that figure is the ferryman, Charon, who transports souls across the five rivers that girt and encircle Hades and to whatever eternity they are considered to have earned. Although the resulting practice of placing a coin in the mouths of the deceased had contemporary parallels and variants - sometimes coins were placed over the eyes - the story of Charon is most famous for the manner in which the dead pay for their own passage to the underworld.
This transactional element, even when it has more to do with contractual symbolism than practicality (Charon, for instance, works in exchange for coins that were never spent), is central to a great deal of mythic and mystical practice: A price must be set and must be paid before a deed can be done. Since this is the case - and since a largely symbolic price can be paid through means that have little intrinsic value - the physical proof of such pacts can be found in seemingly insignificant objects; for instance, the obols exchanged for passage to the underworld. Small enough coin at the time, and common enough even today that their historical significance marks them as mere curios, there is nonetheless a caveat on the worth of those which once served as Charon’s fare.
Rumoured to have been pilfered directly from the ferryman’s coin purse, these obols have been imbued with inextricable magical qualities, each distinct in cause but complementary in nature. The first of these comes from the coins’ being the price in a transaction between the mortal and the eternal and reflects the nature of that deal, the second from their having crossed the veil and returned - carrying with them the stain of all the screams in Tartarus. Where they had been spent for passage, they create the potential for passages; psychic channels through which the living can attempt to initiate contact with the dead, a process catalysed when the obol is placed in one’s mouth (usually held in the cheek or placed beneath the tongue for the duration of the attempt).
Understandably - and somewhat unavoidably - imprecise, the chances of making a connection with any given individual are markedly increased through the presence of persons with whom they shared a close personal bond or with physical contact with objects that they wore about their person over a number of years. This has made these obols a particularly valuable tool for those who claim to be psychics, spiritualists and mediums; their careful use can pepper a career’s-worth of theatricality and fraud with enough moments of genuine insight to win over their wavering sceptics. They might even choose or have cause to practice more honestly, using the coins for every séance or reading, were it not the case that the reality of such contact can be infinitely more harrowing than what is hoped or prayed for.
The obols are also worse than useless if someone is casting about to speak to an unnamed or unspecified presence; if something is in already in or of our world, it has not - by definition - crossed over to another. The coins create intentional lines of communication between worlds and without proper placement the connection is more like an untuned radio, the static a maddening psychic cacophony of overlapping voices that bleed through. Unbidden and uncontrollable, the sheer volume of such desperate communiques can hold a channel open independent of the continued use of an obol, creating points through which plaintive missives and their echoes can sometimes be heard for decades - or more - beyond the initial attempt at a séance or divination.
While the dangers of using the coins can be managed or minimised, even if one is in possession of a trove of Charon’s obols, the mere fact of owning them is enough to incur the cost associated with their secondary characteristic. These coins no longer belong solely to our reality, no matter how they were reclaimed, and they are always and inexorably drawn back to the underworld. The impression of the dead is indelible, and those who truck in the coins’ trade or use risk being pulled bodily out of our world and into the next. This unmooring is gradual, at first, and often begins in sleep. Usually dismissed after-the-fact as uncharacteristically vivid dreams or nightmares, a person will begin to slip between worlds with increasing and accelerating frequency unless and until they are divested of the offending coins.
Assuming, of course, that it is not already too late; at some point the fall becomes inevitable and a person so marked is fated to disappear entirely. They cannot even be reached in the same manner as those with whom they might themselves have communicated, perhaps limited by their continued physical embodiment in places that are more natively inhabited by the essences (call them the souls or the spirits) of the dead. There appears to be a degree of fluidity as to which other realities can be communicated with or connected to via the obols - arguments as to whether apparently innumerable afterlives are formed or shaped (or merely named) by our personal or prevalent beliefs may never cease, let alone be settled - but they do not create passages that can be traversed physically.