For in those days the walls between the worlds were thinner and visits to strange, shining places more believable than they would be now. Also, all these people had heard of the wisdom of the Old Tribes, and most of them had in their veins some of that ancient, knowing blood.
Prince of Annwn, Evangeline Walton
This, not like “once upon a time” or “in the days when wishes still mattered”, comes at the end of the first part of this book. It made sense when I thought about it: Pwyll has returned from his journey, is trying to get his feet back under him in his mortal kingdom and and he decides to come clean and tell e everyone the story of what happened. But, it surely happens at the moment when he begins to tell the tale and the new listeners have to step into the other world and believe.
