J.R.R. Tolkien was considered the greatest translator of his generation, specializing in Celtic as well as Norse works. He drew heavily on his translations while he was writing about Middle Earth, the direct translation of Norse Midgard. Knowing he was a translator, it shouldn’t be too difficult to see the Norse influences in much of his fictional writings – dwarfs (as per Tolkien), elves, giants, orcs, and trolls all come from the Norse as does the concept of humans able to transform into animals. The Celtic side is more difficult to see because we aren’t as well educated there but the wizards, the connection with animals, and the idea of plants thinking and moving probably came from them.
At the end of The Return of the King the remaining elves and wizards take a sea voyage to the west, from which it is made clear they will never return and no human, dwarf, or hobbit (apart from three exceptions) can ever go. That is also Celtic. Hy Breasil, Caer Sidi, Annwn and a half-dozen other disappearing/reappearing islands and fortresses are to be found in Celtic mythology. They were all located to the west, all of them were islands where no one aged, and none of them could be found easily.
What do we know for certain about them? Very little. The argument has been made that Hy Breasil and other mysterious western islands were simply the Irish and Welsh names for Atlantis, back in the nineteenth century and before. The Celtic people, and especially the Irish, were renowned as explorers. An ecclesiastic named Brendan is thought to have sailed all the way to the Americas in the 500s. It’s possible that an earlier explorer made a similar voyage and for whatever reason decided that the Native Americans he found there were ageless.
I pointed out the connection to Tolkien because he was probably more knowledgeable about the mysterious Celtic islands than any person since him. In his descriptions, from The Lord of the Rings and elsewhere, he described the western island as belonging to a different reality, something like the different “worlds” or realms to be found in Norse Mythology. These could only be accessed by certain species. The gods could of course get to any realm but humans were stuck in Midgard, the elves in Alfheim (Elf home), and so forth.
So, is it possible that Hy Breasil was only supposed to be found by certain people? Maaaaybe. So who? The answer to that is simple. A little over a year ago I wrote about Irish mythology and explained that many of the Tuatha de Danaan’s enemies fled and hid after their defeat. Some became known as fairies while others became leprechauns or were known by a host of other names with similar personalities. None of them are said to have fled to an island in the west. However, the Celtic peoples believed that the previous inhabitants of the island had all possessed magical powers and the Fomorians, original settlers of Ireland in myth, seem to disappear after they are finally defeated. If I were to take a guess, I’d say that somewhere there was a belief that they had escaped to an island that was impossible to find. The only thing that was eventually remembered was that there was an island out there that nobody could find and that was home. And as with all the other homes of conquered peoples, in Hy Breasil the people didn’t age.
Just a guess mind you.