The realm of fairy-story is wide and deep and high and filled with many things: all manner of beasts and birds are found there; shoreless seas and stars uncounted; beauty that is an enchantment, and an ever-present peril; both joy and sorrow as sharp as swords. In that realm a man may, perhaps, count himself fortunate to have wandered, but its very richness and strangeness tie the tongue of a traveller who would report them. And while he is there it is dangerous for him to ask too many questions, lest the gates should be shut and the keys be lost.
The original essay on fantasy writing. Mostly discussing actual fairy tales.
It opens with an excursion into what the -- ehem -- Fair Folk are like, before pulling back to treat with the actual subject matter of fairy tales, which is Faerie. He has some legitimate complaints about stories Andrew Lang included. (Though I note that some unquestionable fairy tales -- Catskin, anyone? -- are scarce on magic.) He brushes off the question of origins with some observations about how irrelevant they are, and how the folk tale types can be dangerous, by omitting all that makes one tale differ from the next, and observes that there was always a story, as long as humans actually were involved. (With a comment that when a legend is attached to a historical figure, that doesn't prove it didn't really happen; you need evidence that it was otherwise, or internal reasons that make the story fantastic.) He discusses how things get into the Cauldron, and how the Cooks, not at random, stick in their ladles to draw a story from the soup.
The subject of whether they are for children, of course, gets discussed at length.
Then he gets into the matter so crucial for later fantasy, with his discussion of secondary worlds, and the necessary details, and how it produces an arresting strangeness. And his discussion of the Eucatastrophe, the happy ending.
Much to think upon.