The Fairy Realm

The Fairy Realm — also called Fairyland, Elfhame, Tír na nÓg ('the Land of the Young'), or the Sídhe in Irish tradition — is the parallel otherworld of the Celtic and wider North-Western European folk-traditions: a realm coexisting with the ordinary human world but slightly displaced, accessible through certain openings (hills, wells, fairy-forts, mounds, mist-thresholds, and the mysterious 'thin places' between day and night), and populated by beings whose relationship with humans has always been ambivalent.

The Irish tradition is perhaps the most extensively developed. The Sídhe (pronounced shee) are traditionally understood as the descendants of the Tuatha Dé Danann, the divine race who inhabited Ireland before the arrival of the Milesian ancestors of the modern Irish people; defeated in a semi-mythological war, they retreated not to distant lands but to the síde — the fairy mounds and burial-tumuli that dot the Irish landscape. From this concealed parallel world they continue to interact with the human world, sometimes benevolently, often ambiguously, occasionally with catastrophic consequences for humans who trespass on their spaces or receive their attentions unwisely.

Other North-Western European traditions carry closely related figures: the álfar of Iceland (still legally protected in some Icelandic road-planning contexts), the huldufólk ('hidden folk'), the fair folk, the Wee Folk, the good neighbours. Common features across the traditions include: a distinctly other temporal structure inside the realm (a night spent in Fairyland is famously often a hundred years back home); risky food and drink (accepting fairy food traditionally binds the visitor to the realm); and the specifically eerie beauty of the fairy court itself, described consistently as more vivid, more musical, and more perilous than ordinary reality.

The scholar-writer W.Y. Evans-Wentz's The Fairy-Faith in Celtic Countries (1911) is the classic ethnographic study; more recently, Terence McKenna, Graham Hancock, and others have argued that the fairy-encounter phenomenology overlaps substantially with the DMT- and psilocybin-encounter phenomenology reported today, suggesting a possible continuity between what earlier eras named fairy visitations and what contemporary psychonauts name entity contact. In modern visionary reports Fairy Realm encounters remain widely documented, particularly for experiencers with Celtic cultural background or those in landscapes with strong local fairy traditions.

Sources:
Wikipedia — Fairyland
Wikipedia — Aos Sí