Up and down they went for hours, with nothing to relieve the monotony of the landscape, until finally, when they had topped a higher hill than usual, they discovered a cup-shaped valley before them in the center of which stood an enormous castle, built of purple stone. The castle was high and broad and long, but had no turrets and towers. So far as they could see, there was but one small window and one big door on each side of the great building.
"This is strange!" mused the Scarecrow. "I'd no idea such a big castle existed in this Gillikin Country. I wonder who lives here?"
"It seems to me, from this distance," remarked the Tin Woodman, "that it's the biggest castle I ever saw. It is really too big for any use, and no one could open or shut those big doors without a stepladder."
"Perhaps, if we go nearer, we shall find out whether anybody lives there or not," suggested Woot. "Looks to me as if nobody lived there."
On they went, and when they reached the center of the valley, where the great stone castle stood, it was beginning to grow dark. So they hesitated as to what to do.
"If friendly people happen to live here," said Woot, "I shall be glad of a bed; but should enemies occupy the place, I prefer to sleep upon the ground."
"And if no one at all lives here," added the Scarecrow, "we can enter, and take possession, and make ourselves at home."
While speaking he went nearer to one of the great doors, which was three times as high and broad as any he had ever seen in a house before, and then he discovered, engraved in big letters upon a stone over the doorway, the words:
"YOOP CASTLE""Oho!" he exclaimed; "I know the place now. This was probably the home of Mr. Yoop, a terrible giant whom I have seen confined in a cage, a long way from here. Therefore this castle is likely to be empty and we may use it in any way we please."
...he was dressed all in pink velvet, with silver buttons and braid. The Giant's boots were of pink leather and had tassels on them and his hat was decorated with an enormous pink ostrich feather, carefully curled.So, his castle should be abandoned, right?
He had a wife. And not only was Mrs. Yoop a giantess, she was also a Yookoohoo, in her own words, "the cleverest magic-workers in the world," specializing in transformation.
Mrs. Yoop was actually not upset about her husband being captured and carried off far south into the Quadling Country:
"I must admit, however, that Yoop had a bad temper, and had the habit of knocking over a few houses, now and then, when he was angry. So one day the little folks came in a great crowd and captured Mr. Yoop, and carried him away to a cage somewhere in the mountains. I don't know where it is, and I don't care, for my husband treated me badly at times, forgetting the respect a giant owes to a giantess. Often he kicked me on my shins, when I wouldn't wait on him. So I'm glad he is gone."So he seems to be an abusive husband.
However, with the power of her magic apron, Mrs. Yoop could transform anything into just about anything she wanted. She talks about gathering things from outside the castle and transforming it into food, even mentioning that she made biscuits of some field mice. (So some of the Queen's subjects were eaten by Mrs. Yoop.) She reveals she has turned Polychrome into a canary, and soon turns the Tin Woodman into a tin owl, the Scarecrow into a straw-stuffed bear, and Woot into a green monkey, having made clear to them that nothing she transformed could ever regain its original shape.
Some fans wonder if Yookoohoo magic has to transform an object into something of similar construction. The Tin Woodman can only be transformed into a tin or metal object, whatever the Scarecrow can be transformed into must be stuffed with straw, while Woot and Polychrome can only become other organic creatures. (But what of the field mice made into biscuits?) Other transformations suggest processes of transformations, possibly making slight variations as you go along, such as how Prince Bobo became a goat. (And vice versa.) Polychrome also makes it clear that Mrs. Yoop needs her lace apron to work her magic, so it seems Yookoohoos need talismans to work their magic.
Aside from the messy business of transforming and imprisoning her guests, Mrs. Yoop is an amiable host. However, despite being transformed to be happy with their new forms, the Tin Woodman and his friends escaped anyway when Woot managed to steal the lace apron.
Later, the transformed quartet run into Ozma, who restores most of them, but when it comes to Woot, Ozma realizes that the shape of the Green Monkey must exist in Oz, and she is unable to simply restore him. However, she takes the suggestion from the Scarecrow and Polychrome to transfer the shape of the Green Monkey to Mrs. Yoop. They are able to observe her in a still cauldron making a new apron as she is transformed.
And then, she never reappears in the Famous Forty Oz books.
There was an Oziana story in which she escapes and frees her husband, only for the Green Monkey shape to be transferred to Mr. Yoop and Mrs. Yoop becomes a turtle.
However, recently Paul Dana's The Law of Oz and Other Stories and The Magic Umbrella of Oz, the nature of Yookoohoos—and of Mrs. Yoop—is explored further. Paul confirms that yes, Yookoohoos need to make a talisman to harness their magic with. Mrs. Yoop—who he names Moyna—was not the most skilled Yookoohoo and couldn't revert her transformations. She serves as one of the antagonists in both "Time Travelers of Oz" and Magic Umbrella.
However, Paul leaves Mr. Yoop shut up in his mountain prison, which reminds me of a joke I made once. Mr. Yoop said he once ate a monkey, so if he met his wife in her current form, he might eat her.
And she'd be sure to disagree with him.