Tír na nÓg Old Irish: Tír inna n-Óc "Land of the Young" is widely known as an Otherworlds in Irish mythology and in the story of Oisín. Oisín was one of the few mortals who lived in the land of Tír na nÓg and was said to have been brought there byNiamh of the Golden Hair (Niamh Chinn Óir). It was where the Tuatha Dé Danann settled when they left Ireland's surface, and was visited by some of Ireland's greatest heroes. Tír na nÓg is similar to other mythical Irish lands such as Mag Mell and Ablach.

Tír na nÓg was considered a place beyond the edges of the map, located on an island far to the west. It could be reached by either an arduous voyage or an invitation from one of its fairy residents. The isle was visited by various Irish heroes and monks in the echtrae(Adventure) and immram (Voyage) tales popular during the Middle Ages. Contrary to popular assumption, Tír na nÓg was not an afterlife for deceased heroes, but instead, a type of earthly paradise populated by supernatural beings, which a few sailors and adventurers were fortunate enough to happen upon during their journeys. This otherworld was a place where sickness and death did not exist. It was a place of eternal youth and beauty. Here, music, strength, life, and all pleasurable pursuits came together in a single place. Here happiness lasted forever; no one wanted for food or drink. It is roughly similar to the Greek Elysium, or the Valhalla of the Norse, though with notable, distinct and important differences.