In any city, in any country, go to any mental institution or halfway house you can get yourself to. Ask the worker behind the front desk to see “The Holder of Respite.” If you're lucky, you'll be led to the back of the building and shown a rotting wooden trapdoor. The worker will open it for you. Once you descend, there's no going back.
The trapdoor leads to a stony labyrinth -- one devoid of windows, and filled with the kind of golden-brown dusty light one might see in an attic in the afternoon. Don't dwell too long on the light; stay alert, and search for the Holder, as he is already searching for you.
He is a hulking, twelve-foot-or-taller beast with the body and legs of a man, but the head and feet of a bull. You won't be able to see him until he wants you to, and he doesn't like his prey to see him until it's too late. Keep your wits about you; if you do not defeat this Holder, you shall become his next meal.
No matter how skilled or unskilled you are at combat, if you manage to fend off the beast's initial blow, the two of you will be evenly matched thereafter. Continue your battle, and when you are ready for it to end, ask the beast, “Where is it safe?” Upon hearing this, he will pause for the briefest of moments, giving you an opportunity to strike before he responds. Attack; if you let him give his answer, you will find yourself horribly outmatched when the fight resumes.
You cannot kill this beast -- not permanently, anyway. Time will eventually heal all wounds that you inflict, but you can strike him down for long enough to take what you have come for. Assuming you manage to render the Holder inert, approach his body and check the hand that wasn't carrying the axe. It ought to be tightly clenching a Thumbtack. If not, you'll have to search the ground around where you fought.
Stick the Thumbtack into something, and the stuck item will be hidden from all you wish to hide it from.
The Thumbtack is Object 158 of 538. Use it sparingly, lest what it hides fade from view forever.