Presto! The electric motor whirrs, and the stately Federal facade of the 13-room Kentucky mansion rises majestically, revealing the hallways, kitchen, living rooms and upstairs bedrooms. Everything is immaculately in place—beds made, a bouquet of daisies on a coffee table, silver place settings on the dining-room table, a living fern on the 18th century drum table, even a copy of The National Geographic in the sun porch.

A well-run house? Yes. But as a miniature dollhouse, fantastic! Mistress of it all is 16-year-old Cornelia Whitney. But the guiding hand is that of her mother, Marie Louise Whitney, fourth wife of Cornelius Vanderbilt (Sonny) Whitney, the multimillionaire sportsman-industrialist. Marylou was a bride of two weeks when Sonny first brought her to Maple Grove in Lexington, Ky. Worm-eaten floorboards gave way beneath her feet and there were even snakes in the basement. Marylou took Sonny's hint that she "make some changes," and turned Maple Grove into the show-place of the bluegrass country.

Six years ago, Marylou listened again when Cornelia, then 9, said "she wanted a dollhouse that looked like our home," and rebuilt Maple Grove all over again—this time in miniature. The second effort proved by far the more arduous. Headed by Maple Grove's carpenter, Ernest Hughes, who turned out to be a master model maker, the whole staff was soon whittling, sawing and hammering. (As Marylou pointed out to Sonny, "The men didn't have enough to keep them busy on rainy and snowy days during the winter.")

Using discarded dentists' tools for work too fine for fingers, the men turned out American antiques to scale; the women became expert at making coat hangers out of paper clips and sewing draperies and clothes. Meanwhile, Marylou threw herself into tracing Maple Grove's history, from a 1782 fort. (The result, just published: Cornelia Vanderbilt Whitney's Dollhouse, $25).

"I get goose pimples when I think about that house," says Mrs. Whitney, in New York to exhibit the dollhouse for charity. "The rooms are so full of happiness." Happiness isn't all. The rooms require a daily dusting (even the silver must be polished). And hearing that the lady of the house may hit the lecture circuit, her three Kentucky staffers shudder. "It took a whole week to pack the dollhouse," grumped Mrs. Jouett Redmon, wife of Maple Groves' caretaker "and another week to reassemble everything."