Keychain (plain and simple — no pun today, sorry)

Behold my painfully fabulous new keychain:

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It is new only insofar as my possession of it goes. I am quite sure it is rather old, given that it was described as “vintage”, and I never question anything I read or anything anyone tells me. (For instance, for many years I scoffed at the notion of the Loch Ness Monster and would loudly proclaim “Bunkum!” at the mere mention of the phenomenon. However, five years ago I had to eat my words [fortunately “Bunkum!” was dipped in dark chocolate and dusted with the finest of diamond dust] when I saw her in a bar on Columbus Avenue. I have learned my lesson.)
With this keychain, I got more than I bargained for. Although nowhere in its description was the word “magic” used, I find that my keys, which before had only opened the locks to which they had originally been assigned, have led me to other locations where they open doors I never would have had occasion to use before. The key that used to open only the front door of my building now opens the door to an executive wash room (the men’s, alas) somewhere on East 53rd Street (I cannot divulge the exact address or what I was doing there). The one that opens the door into the front hallway now also gives me access to the tear-stained diary of a 14-year-old with an eating disorder somewhere in Poughskeepsie (I cannot reveal her name or how I got her diary). The key that opens the door to my actual apartment also opens Grant’s Tomb (I cannot tell you who is buried there). And my mailbox key still only opens my mailbox, except now when I reach inside I am met only with a ham sandwich from an old automat.
I got it for a song, which, incidentally, is only appropriate given that it plays a song, which delights me even more than the keychain’s good looks and surprise magical abilities. The song is brought to life by winding up the keychain in the back. Look:

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I invite you to guess the name of the song. I will not give any clues but will gently remind you that this is a vintage keychain, so do not waste your time guessing anything that has only ever been released in mp3 format.
(P.S. Real life friends who already know: Don’t go spilling the beans. Thanks.)