Holden spends a good deal of time describing the Museum of Natural History in New York City, a place he went every year on school field trips. He has very fond memories of this museum. One quote that alludes to the sense of innocence he felt there is the following:
Nobody gave too much of a damn about old Columbus, but you always had a lot of candy and gum and stuff with you, and the inside of that auditorium had such a nice smell. It always smelled like it was raining outside, even if it wasn't, and you were in the only nice, dry, cosy place in the world. I loved that damn museum.
As the quote suggests, the museum was a place of comfort, warmth, and security to Holden. Innocence is conveyed through the images of candy and gum, as well as with the repetition of the child's term "nice." In an unreflective way, Holden felt good and at home in the museum when he was a kid.
A long quote that conveys the return to childhood innocence that Holden finds in the museum is the following:
You could go there a hundred thousand times, and that Eskimo would still be just finished catching those two fish, the birds would still be on their way south, the deers would still be drinking out of that water hole... Nobody'd be different. The only thing that would be different would be you. Not that you'd be so much older or anything. ... You'd just be different, that's all. You'd have an overcoat on this time. ... Or you'd just passed by one of those puddles in the street with gasoline rainbows in them.
The fact that the museum stayed the same gave Holden a sense of stability as a child. It represented a world in which he might change—in small, innocent, childlike ways—but the universe as a whole would be unchanging. It represented the time before Allie died, the moment when Holden realized the entire ground of one's existence could shift in an instant.
Holden longs to return to that time of innocence. He wants life as a whole to be like the Natural History Museum, where the dioramas never change, where everything can be relied on to be the way it always was. As he comes to grips with growing up, he both clings to that lost innocence, and yet struggles to come to grips with the inevitability of change and loss.