Realm Of The Dead
Underworld, Hades
noun
The underworld dirt is another word for the realm of the dead, underworld, or Hades. Like the word 冥界 (also in this level), it's rather poetic, and mostly used in written contexts involving spirituality, Buddhism, and ancient mythologies.
There are a few set expressions that only use 冥土, though. One example is 冥土の土産, "a souvenir to take to the realm of the dead". It refers to something abstract that is so valuable, it's worth taking to the underworld, such as the solution to a great mystery, or a happy memory.
Another expression is 冥土の旅支度, which means "preparations for the journey to the realm of the dead", and can refer to the preparation of the deceased before a funeral, as wells as certain preparations made by Buddhists while they're still alive.
You'll also see this word written as 冥途 sometimes.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
どんなにお金を稼いでも、冥土には持っていけないんだよ。
No matter how much money you make, you can't take it with you to the underworld.
「冥土の土産に教えてやるよ。」と、男は銃を構えたまま秘密を話し始めた。
"I'll tell you something that'll be your souvenir for the realm of the dead" said the man, and began to tell me his secret, keeping his gun pointing at me.
仏衣や死化粧などの冥土の旅支度をして、故人は来世へと向かいます。
After preparing for the journey to the underworld by dressing the body in Buddhist robes and applying makeup for the deceased, they will go on to the next life.