Among the fantasies of the New York child, in addition to the ones about sleeping overnight in Bloomingdale’s mattress department and being left alone for two hours in Dylan’s Candy Bar, none is keener than that of slipping inside one of the glassed-in dioramas at the American Museum of Natural History. Each of them, after all, contains not just an instructive picture but a little world, sealed off unto itself, and the idea of entering, not to say violating, the timeless space of gorillas or wolves or mountain lions is intoxicating.

This actually became possible not long ago when an eleven-year-old we’ll call Rose got to walk inside the dioramas, on the occasion of the thorough conservation and restoration that the museum is giving to its entire Hall of North American Mammals. The exhibits there contain the less dramatic, but still poignant, local animals—not gorillas and whales but brown bears, bighorn sheep, and American bison—and are considered, as someone at the museum said flatly, “the greatest natural-habitat dioramas in the world.” Not the least of the reasons for this distinction is that the backgrounds, easily missed on an exhausted trudge to the cafeteria, are among the finest landscape paintings in New York. They are most conspicuously the work of a legendary scene painter, James Perry Wilson, the Raphael of the animal diorama.

“When Wilson and his contemporaries were working, dioramas were the state-of-the-art virtual reality of the day,” Steve Quinn, the senior project manager of the restoration, and a diorama man, said to Rose as she entered the work-bustling hall. He was accompanied by Robert Voss, the curator in charge of the conservation. “They were windows onto other worlds and landscapes, and the engineering that went into making them completely convincing is still astounding now,” Quinn said, adding that when the hall opened, in 1942, just after America’s entry into the Second World War, “the dioramas became a kind of patriotic pageant, a picture of our land and our values. They stood for America.” The task at hand is to restore the works to their original state while gently emending wall labels and the like to reflect new knowledge about the animals who gave their lives, and skins, for the depictions.

Rose was taken by the absence of glass. It had all been removed from the dioramas, and plywood planks and scaffolding erected, and this somehow, she explained, made the animals inside seem less like animals frozen in a museum than like animals frozen in time—hypnotized, in a flash, by a visiting alien. “And you can see them on all three sides,” she added.

To walk gingerly inside the dioramas is also to see how intricately, and how cleverly, Wilson’s paintings interconnect with the taxidermic objects. From a distance, the paintings have a piercing, Kodachrome-like accuracy. Up close, one sees that their fidelity is impressionistic: Wilson worked with painterly certainty to sum up atmospheres and rock forms in a few decisive strokes. The virtual-reality engineering of the dioramas, newly revealed by modern lighting, is far more elaborate than even a watchful child might detect. Though the animal skins are all real, and usually taken from the very site depicted, the grasses and leaves and trees that surround them are made of plastics, plasters, paper, and beeswax, painstakingly molded and painted and pinned together. (They’re being restored, too.) Mirrors are inserted into some of the elks’ mouths to create a more lifelike…something or other.

The key to the illusion—the equivalent of “selling the shot” in today’s special effects—is what is called the “tie-in”; that is, the small, vital area in the rear of the diorama, the brief zone where the three-dimensional artifacts meet the sloping, painted background. If the tie-in is done subtly enough, Quinn explained—a matter mostly of fine-tuning hue and shade and tone—the diorama works, the illusion compels, and the visitor is suddenly in Yellowstone or Alaska. If it doesn’t, she remains on the Upper West Side.

Clear favorite among the dioramas? The eerie, “Twilight”-ish, moonlit wolves, in which, despite the gloom, you can just make out the hoofprints of the deer that the wolves are hungrily chasing. Most memorable moment? “The mystery of the mirror in the moose’s mouth,” Rose announced, giving birth to a judgment and a tongue twister, all at once.