In any city, in any country, go to any mental institution or halfway house in you can get yourself to. When you reach the front desk, ask to visit someone who calls himself "The Holder of the Center." The worker will meet your gaze suddenly, and close his eyes. He will point his finger in a random direction; follow his direction as given, and your soul will be sundered from your body, for demons unimaginable to do what they will with both. You must go in a straight line in the opposite direction instead. Whether or not it was there before, you will come to a nondescript metal door. Enter, and you will find yourself in a circular room, the walls lined with doors. Save for one, they will be identical. The other doors will call for you to open them, but you must only open the unique one, lest you wish to sacrifice your sanity.
When you open the unique door, you will come to a perfectly spherical room, perhaps a hundred feet in diameter. The surface around you will be solid, but will appear to shift around, as if made of mercury. Do not fear falling as you step through the door, as gravity will hold you to the surface. Walk straight ahead. You are free to look around you for now, but do not stray from the line you walk, or the surface will liquefy below your feet. It will not harden until you are fully submerged, and your lungs filled to the brim, and you will remain where you are for eternity, never dying, and forever choking on the cursed metal. Continue in this manner until you have gone full circle and returned to the door. Stand on the door, and look straight up. What you see at the center of the room, equidistant from all points on the surface, is what appears to be human, but at the same time, does not. It will be shapeless and sizeless, yet somehow recognizable, despite having no front or back, no top or bottom, no left or right. Try not to comprehend what you see or your mind will literally ignite where you stand. Stare at it for five minutes without breaking your gaze, and it will turn to face you. You will understand when it happens. Look away before then, and it will consume you before you know what has happened, though you will feel unimaginable pain before it ends. When it faces you, you must ask it one question, for it will respond to no other: "Where will they meet?"
The entity will answer in the voices of all who have ever lived speaking in unison. It will speak of all who have sought them before you, and it will tell you in every last graphic detail how they met their fates. As it speaks, the surface of the room will slowly begin to glow and turn the color of blood, and shape itself into a tapestry of the faces of those of whom the entity speaks.
When the answer has been given, you will feel the palm of your right hand burn with the fires of a thousand suns, but do not look, for this is where they brand you. To look upon the mark now will cause it to become a hole, through which you will bleed out of reality itself, your every molecule spread across an oblivion filled with horrors no mortal tongue, real or imagined has ever had or will ever have words for; all that can be said of this place is that even the souls of the damned in the most torturous pits of hell would pity your fate. If you have maintained your eye contact with the entity the entire time, it will shrink into its central point, and when it is as nothing, all will go black. When you regain your sight, you will be in the alley behind the hospital. It is now safe to look into your hand.
The mark is number 47 of 538, and it is where they will come together.