Two famous New York museums play a part in The Catcher in the Rye: the Museum of Natural History and the Metropolitan Museum of Art.
Holden has happy memories as he anticipates visiting the Museum of Natural History. He often went there as a child. It was a point of stability for him, because nothing ever changed. The dioramas of Eskimo and Indian life were always the same every year, as was the film about Christopher Columbus. Holden associates the museum with his secure childhood before his brother's death. He ruminates that:
Certain things they should stay the way they are. You ought to be able to stick them in one of those big glass cases and just leave them alone. I know that's impossible, but it's too bad anyway.
However, when he arrives at the museum, he decides not to enter. It's very likely that he doesn't want to risk having his pristine childhood memories ruined:
Then a funny thing happened. When I got to the museum, all of a sudden I wouldn't have gone inside for a million bucks. It just didn't appeal to me--and here I'd walked through the whole goddam park and looked forward to it and all. If Phoebe'd been there, I probably would have, but she wasn't. So all I did, in front of the museum, was get a cab and go down to the Biltmore.
Later, he tells Phoebe to meet him at the "museum of art." From the description he offers, he means the Metropolitan Museum of Art. While waiting for Phoebe, he helps two boys who are playing hookey from school find the "mummy" exhibit, which involves walking through the reconstructed walls of a pyramid. The boys get frightened and run off, but Holden continues. He is disillusioned, however, when he notes someone has written an obscenity on a wall: this is the kind of shock he no doubt wanted to avoid by not entering the Museum of Natural History.
Museums represent safety, childhood, and happy memories to Holden, which is why he likes the Museum of Natural History. But as he finds out at the Metropolitan Museum of Art, even museums, like so much else, can force him to confront a loss of innocence.