I return to re-read Tolkien's novel-fragment The Notion Club Papers every year or so; and on the current encounter it struck me that - given the NCPs history of having been read-to The Inklings, as a light entertainment initially (later ripening to an extremely ambitious conception - perhaps the most ambitious work Tolkien ever projected), the very first significant incident of the book seems likely to refer back to an actual incident in an Inklings meeting.
What happens is that Ramer (who is substantially a Tolkien alter ego, being a philologist and science fiction/ fantasy writer) has just read a story to the Notion Club.
The club responds to Ramer's story with various jovial and satirical comments, the substance of which is that they much liked the story itself - which we don't know much about, but which apparently was set on another planet; but found the 'frame' describing getting-to and back-from this planet unconvincing and contrived, while the story itself had the ring of truth.
Indeed, some of the club members intuit that the story was not entirely fictional, in the sense that it seemed as if Ramer had actually 'been there', in the world he described.
Later, Ramer reveals that this is true - he has actually visited this other planet, in reality - but in a dream.
If we suppose that Tolkien was writing this episode based-upon an actual occurrence in an Inklings meeting, which seems likely; what story of Tolkien's might it refer to?