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 see someone who calls himself "The Holder of Envy". Should the worker look like he'll cry, and starts nodding softly, he will take you to a basement with a steel hatch and tell you to walk down. The worker will close the hatch and leave you with a loud noise. Once you've walked down the stairs, you'll be in a long, dark hallway. On the other side is the door you're headed to. This black necklace is object 456 of 538. Never bring the objects together.