In any city, in any country, go to any mental institution or halfway house you can get yourself to. When you reach the front desk, ask to visit someone who calls herself "The Holder of Song." You will then be guided to a long staircase that spirals higher than the building stands. At the stairs' summit is a door.
As you open the door, a sudden wave of heat will pour out from the hallway beyond it, and wash over you. Proceed down the hallway. As you walk, the air around you will grow increasingly frigid. When you feel as if you are encased in ice, you must stand perfectly still, remain silent, and listen. If, after a few seconds pass, you hear a baby crying, turn and run. No harm will befall you, but the infant's cry will follow you wherever you go. If you hear it for the rest of your life, count yourself lucky; if and when it stops, your firstborn child will die.
If you do not hear a baby's cry, wait for the hallway to grow warm once more, and then proceed to the door at its end. Enter.
The room beyond will be awash in green light. At its center will be an old woman turning the handle of a silent music box. Her legs have both been severed at the knees. When you speak to her, you must look her in the eyes. She hides a spear fashioned from the bones of her legs; break eye contact, and she will impale you with it and leave you to bleed to death in seemingly unending agony. She will respond to only one question: "What was the song they used to play?"
The old woman will begin to sing in a language not of this world. Her melody will be the most beautiful one you have ever heard, bringing peace and serenity to your mind, body, and soul. You will find yourself vividly imagining a band of carefree children playing and singing, innocent as can be... And within minutes, the scene will eventually take a horribly sinister turn. The children will begin to fight each other, and their conflict will quickly escalate to the most brutal, lethal violence you can conceive of. They will impale each other on wooden poles, disembowel each other with sharp rocks, and even rip flesh from bone with their bare hands. You will witness these children, now merely tattered doppelgangers of themselves, spreading death and destruction more horrific than you could ever imagine on your own. You will see a naked boy, drenched in blood, singing with delight as he runs through a hellish wasteland, pursued by unspeakable monsters. They will overtake him and utterly destroy him, the song still issuing forth from his shredded lips all the while.
...Yet, inexplicably, you will remain calm and peaceful even as you watch this unspeakable brutality.
When these horrific visions end, an intense pain will stab at your chest. Your heart will feel like it is about to explode. Do not let the agony break your focus, and do not break eye contact with the old woman, lest you invite a fate so horrible that an exploding heart seems lovely by comparison. If you remain steadfast in your gaze, the pain will eventually cease. The woman will stand up (though, with your eyes still focused on hers, you will know not how) and place the music box in your hands.
The music box is Object 6 of 538. When its song plays again, they will all come together.