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 Time". The worker will act like he doesn't know what you're talking about, first treating it like a joke, and then threatening to call security. Persist for long enough, and he will ask if you want to see the doctor.
If you say no, you will be killed instantly. Many who have spoken to the Holders choose this, for it is the ultimate mercy compared to the horrors you face. There is no other escape.
If you say yes, you will be bathed in brilliant blue light. You must remain perfectly still, or else you will be cast out of time, both frozen in an instant and aware of the eternal burn of entropy, and forever experiencing every moment of your decline into insanity all in one moment.
Remain still until you hear a sound, an ethereal blend of musical and metallic. It will increase slowly, the sound and light seeping into your mind and carrying you away with it. If you survive with your sanity intact, you will long for that sound for the rest of your life.
When the sound and light fade, you will find yourself in a large room made of metal. One man will stand in the center of it, his appearance and clothing constantly changing. He will speak incessantly, telling stories about every time and place in the whole of the existence of the universe. He will not stop speaking unless he is asked, "When will they come together?"
He will stare at you and hold out his hand as he shifts through different appearances. You will feel an overwhelming temptation to take his hand, though part of your mind will fear what awaits you if you do. If you take his hand, you will experience each of his stories as though you lived them, and in the millennia that pass before he releases you, you will fall into insanity.
After his twelfth shift into a new appearance, his thirteenth life, the man will answer your question, and a small key will appear in his hand.
The key is Object 26 of 538. Pray that you never find what it unlocks.