How do Irish voyage tales describe journeys to the otherworld?

In early Irish literature, voyage tales known as immram (or echtrae when focusing on otherworld journeys) describe the otherworld as a realm of eternal happiness, often imagined as islands in the sea or an underground location. This realm, referred to as the "Land of the Living," "Delightful Plain," or "Land of the Young," is characterized by the absence of sickness, aging, and death, where time passes so slowly that a hundred years may feel like a single day.12

Journeys to this realm are often depicted through specific motifs:
* The Call: A beautiful girl may approach a hero, singing of the happy land, leading him to sail away in a boat of glass.2
* Magic and Mists: Heroes may set out on a quest and encounter a magic mist, eventually finding a palace where they are welcomed by figures such as Manannán or Lugh.2
* Temporal Distortion: Upon returning from these voyages, heroes often discover that vast amounts of time have passed, leaving their companions dead or their journey forgotten by all but ancient sources.12
* Wondrous Encounters: Tales like the Immram Curaig Mael Dúin describe voyages to numerous islands featuring strange beings, structured societies, and supernatural challenges.3