The underground world is vast and boundless, and human exploration of the underground world can be said to be only in the shallow area. Catherine and As, for example, once entered the Magma Cavern - an open entrance to the underground world - to hunt down a magma red bull that often roams the surface.

The environment in the magma cave is very harsh, with sulfur gas everywhere, all kinds of lava rivers are dense, and the temperature is hot and dry. However, this is only a common form of the underground world, and there are many strange areas that humans have not yet set foot in. For example, the abysses located in the depths of the underground world and ruled by demon lords.

At present, the main understanding of the underground world comes from a book called "Travels in Stealing Stones". The book was written around the time of the first millennium of chaotic humanity and was written by "The Great Thief Dipp."

In the book, Dipu tells the story of how he dived into the underground world through the entrance to the surface world (later some scholars believed that this entrance was a magma cave), and went deep into the underground little by little, successfully blended into the hard stone abyss, stole the large diamond of the demon lord Diamund, and escaped various pursuits, and finally returned to the surface safely. The story itself has all kinds of logical holes and over-exaggerated, outrageous plots, and has little merit from a literary point of view.

But through such a story, Dipu does depict a strange underground world. Therefore, the historical contribution of "Travels in Stealing Rocks" lies in the fact that it shows another ecological environment for mankind for the first time in complete and detailed form. And as the powerful men of various countries entered the underground world one after another, more and more evidence showed that Dip's description of the underground world was basically in line with the real situation.

As a human being who can move freely in the underground world, the deeds of this great thief are not found in various historical documents and legends, and there is no real record of his life. Except for a copy of "Travels in Stealing Stones", "The Great Thief Dip" seems to have never existed in this world.

The thousandth-year historian Els, in his famous book "Sorting Out the Millennial Age", asserted that the great thief Dipper was just a pseudonym and that his real person did not exist. The description of the underground world in "Rock Stealing Travel" is derived from the exploration of the underground world by the dwarf civilization, one of the four great civilizations of ancient times.

As soon as this statement emerged, it was immediately criticized by the academic community. One of the most direct rebuttals is: There was an obvious historical gap between the four ancient civilizations and the human era. How did the dwarven civilization, which is between the goblin civilization and the ancient elven civilization, preserve their cultural information, and it happened to be obtained by the great thief Dipu and written into a book?

In order to support his own opinion, Ells also proposed that "Travels in Stealing Stones" was originally written during the period of dwarven civilization. It actually depicts the fall of a dwarven civilization, and for some reason uses a curved pen. The author of the book, whom Els believes to be a bystander living during the period of the Dwarven civilization, witnessed the dwarves marching into the underworld, fighting the demons of the Hard Rock Abyss, and finally causing the catastrophe of extermination.

For this reason, the historian also starts with specific passages in "Travels in Stealing Stones". Compare with existing dwarven cultures. He has published a series of sensational academic papers. In particular, his speculation about the reasons for the fall of the dwarven civilization. It has been recognized by many scholars. However, Ells's point of view has always had two flaws: first, how did "Rock Stealing" come down, and second, who its author was.

To this day, the mystery of the origin of the great thief Dipp has been a major mystery in the academic world. Quite a few papers are published every year. Conduct research on this great thief. It's just that a convincing argument never appears.

However, it is interesting that the influence of the great thief Dipu in the people far exceeds his contribution to scholarship. It is said that the profession of thieves was officially recognized because of "Travels in Stealing Stones" and gradually developed.

Didn't Catherine meet a thief in the magma cavern who wanted to dive into the Black Abyss and steal the Horn of Fear?

But in today's Eastern Continent. A place like a magma cave is no longer an underground world in the true sense of the word. According to the current academic definition of geography, areas such as magma caves are considered to be the middle ground between the surface and the underground world.

These intermediate strips are measured in breadth, ranging from tens to hundreds of kilometers. The reason for this definition is because of the real underground world. There are all kinds of powerful beings with intelligence. They will establish their own sphere of influence in the underworld. And the borders of these spheres of influence reach as far as the edge of the middle ground.

Human exploration of the underground world often stops at the middle ground. Because after continuing to go deeper, you will encounter obstruction and attacks from underground forces. For example, after passing through the magma cave, you will enter the sphere of influence of the so-called "Red Devil Abyss".

The Red Devil Abyss isn't really an abyss, but there is a Red Devil Lord there. And the "Red Devil Lord" is not a real Demon Lord, it is just a demon who calls himself the "Red Devil Lord".

If the Red Devil Abyss is understood in a human way, it is about a small country in the underground world. Its king is the Red Devil Lord. Since the magma cavern is within the kingdom, there is a certain border dispute between the Red Devil Abyss and the kingdom. So the armies stationed outside the magma caverns have a completely different political meaning compared to the armies of the rest of the kingdom.

Catherine also learned about these things after she was rescued from the magma cave by Gisling and Sword Saint Swo. For this reason, the mage also read several books dedicated to the underworld, including a booklet about the Red Devil Abyss that Ghisling had lent her to read.

Catherine was glad that the Red Bull hunt had almost failed to cause diplomacy between the surface and the underworld.

This personal experience gave Catherine a lot of ideas about the underground world, and played a good role in guiding her current deal with the Demon King.

Catherine didn't know where she was at first, and even the sight of the Lady of Reason was limited by her first will. The mage's own memories are currently divided into two periods, the first one until she and Ace entered the Paradise of the Brave for the second time, and the second one is after awakening in the Kingdom of God until now.