Listening to Tirian's story, Duncan fell into a short period of thought. After half a minute, he raised his head and spoke thoughtfully: "So, in order to satisfy her desire for exploration, she started a 'Dive Plan', and the essence of this plan is actually not to explore the warp at all, but just... literally 'dive into the deep water'?"

At this point, he paused, and felt that there were many strange things about this matter: "But if that's all, how can this plan be related to the Lost Homeland? The warp that the Lost Homeland went to and the deep sea that the Frost Queen wanted to explore are two completely different concepts. Those rebels should not be unable to even distinguish between them..."

Tirian did not answer directly, but suddenly threw out a question: "Don't you find it strange? If it is just diving into the water to explore the sea conditions deep in the city-state, how can it be called a 'taboo'? The port builders and offshore fishermen of the city-state often dive into the water for work. It is very common to dive more than ten meters or even dozens of meters in safe waters. Why did the Frost Queen's 'Abyss Plan' become a taboo?"

Duncan's eyes gradually became serious: "...How deep did you dive?"

"Very deep. I don't know how deep the queen finally dived. I'm not a scholar. I just participated in some peripheral assistance as a naval commander, and I was no longer directly involved in the operation in the second half of the plan. But from what I know, before the plan began to become... 'wrong', their manned submersible reached a depth of at least one thousand meters underwater, and they kept breaking this record."

One thousand meters underwater...

Duncan quickly sorted out the knowledge he knew in his mind - on Earth, this seemingly insignificant number is actually the maximum diving depth of many advanced military submarines, and the diving depth of most military submarines is only four or five hundred meters. As for those "extreme deep diving records" of thousands of meters or even nearly ten thousand meters, they are basically completed by special submersibles in a short period of time. The equipment requirements are extremely high, and often only unmanned equipment can be used.

At that time, the Frost Queen's manned submersible had already reached the "one thousand meters" threshold. Considering the industrial level of this world half a century ago, even with the assistance of some extraordinary powers, this was already an astonishing number.

And behind this astonishing number...there is obviously something even more "astonishing".

Tirian just mentioned that the plan began to become "wrong" in the later stages, and Duncan did not ignore this word.

He looked at Tirian, his eyes darkening. "I wish to know the details of the entire exploration plan - tell me how much of your involvement you have."

It seemed that because he had already answered many questions and was used to this kind of communication, Tirian did not hesitate for too long this time. He fell into recollection and slowly spoke in his recollection:

"...Except for Frost's Abyss Project, the conventional diving depth, or 'safe water depth', recorded by humans is 150 meters, and is limited to the offshore area. Our project also started at this depth, and it went smoothly until 300 meters.

"It was already very dark. The sunlight on the sea surface could not penetrate such a thick body of water. The high-power lamps carried by the submersible could only illuminate a small area. In order to explore the 'appearance' below the city-state island and to avoid some dangerous 'creatures' in the distant sea area as much as possible, such as deep-sea offspring, we let the submersible dive along the coast and move close to the offshore area of ​​the island. I still remember the scene described by the explorer after he came up...

"He said that the island was like an ugly, rough pillar underneath, covered with thick limestone sediments, and that some strange creatures lived in the pits of the sediments, and apart from the 'pillar', there was nothing around, only darkness."

"Is there a pillar under the island?" Duncan couldn't help interrupting Tirian. "Not a gradually expanding supporting structure, but a pillar?"

"Yes, at least that's the case with Frost," Tirian nodded. "What's the problem with that?"

Duncan shook his head: "...No problem, go ahead."

Tirian sorted out his thoughts and continued his previous recollection: "That was the scene seen at a depth of about 300 meters, which was also the limit depth of the first submersible. After realizing that this depth was far from enough to explore the deep sea, the queen ordered scholars to build a second submersible. This submersible was very successful. It dived into the water at a depth of 800 meters in one breath. Through the half-meter thick high-strength glass, the explorers saw... still a pillar, a straight pillar.

"Of course, compared to the radius of the city-state itself, this 'pillar' that is at least 800 meters long is still very short in proportion. Rather than being a pillar, it is more like a regular disc-shaped base supporting an island.

"Then we built a third submersible. Due to technical limitations, the improvement of this submersible was far less than that of the second one. It had to dive carefully to challenge the record of the second submersible. And it was during the slow dive, meter by meter, that we discovered something.

“The ‘pillar’ below the city-state is actually only 850 meters ‘long’, and below that, there is nothing.

“The entire structure is floating in the sea water.”

Tirian paused and looked up into the eyes of the Duncan. "Now you understand why I said it was more like a disk than a pillar?"

Duncan frowned tightly. He did not speak, but quickly sketched the entire structure in his mind according to Tirian's description.

People in the deep sea era lived in city-states. Duncan initially had the impression that these isolated islands on the sea were crowded and small, but in fact, as fully functional and self-sustaining places of residence, these city-states were destined to have a certain "size basis". Although there were some small islands, the "basic radius" of most of the big cities that could be named had reached more than ten kilometers or even dozens of kilometers. As the largest city-state in the Frigid Sea, Frost would not be smaller than this number.

Corresponding to this huge offshore structure is its "base" which is "only" 850 meters deep underwater. The explorers initially saw the underwater part of the city-state extending straight into the deep sea at a depth of 300 meters, and intuitively imagined that this was a pillar reaching the "bottom of the sea", but in reality, in terms of proportion, the shape of this "pillar" is more like a thin round cake.

The huge city is placed on this "round cake".

As Tirian described: The entire structure floats in the sea water.

But after imagining this model, a huge doubt emerged in Duncan's mind -

Is this true in every city-state?

If every city-state is like this, a "floating object" without foundation, then how can they be so stable? If the "stability" of the city-state itself is due to its large scale, then how can we explain why the relative positions of the city-states are also so stable?

Amid the rolling waves of the vast ocean, these "floating islands" have never changed their positions. Why is that?

Duncan expressed his doubts, but Tirian just shook his head. "We also had doubts about this, but in the end we could not figure it out. Compared with what happened later... the question of 'how did the city-state float on the sea' is irrelevant."

"What happened next?" Duncan couldn't help but wonder, "What happened next? What did you see in the deep sea?"

"Later... Submersible No. 3 continued to challenge the extreme depth. It took us nearly two years to push this record from 850 meters to 950 meters. As you can imagine, during this dive, the submersible was gradually moving away from the city-state's 'base' - remember what I said at the beginning? In order to avoid problems in the open sea, we let the submersible dive in the 'offshore safety zone' close to the coast. During this whole process, the submersible was actually always close to the city-state and its underwater 'structure', but as the dive continued, the explorer moved away from the 'base', and things started to go wrong.

"Hallucinations, visions, strange lights appearing in the sea, someone knocking on the hull, and even turning the handle of the gate. The deeper you dive, the more serious these situations become. Even explorers with special training and strong wills begin to feel tremendous pressure with every dive, and the protective effect of the holy oil, sacred books, and scripture cloth they carry with them becomes less and less obvious.

"Of course, up to this point, this is all within our expectations. Exploring the unknown requires facing challenges in terms of willpower. Scholars who explore the spirit world and the abyssal sea often encounter this kind of trouble. So we are still continuing, but we have strengthened the explorers' mental protection according to the most stringent standards.

“The problem came when I challenged 1,000 meters from 990 meters.

"Submersible No. 3 suddenly sent out an emergency ascent signal, and then rushed up like crazy by emptying the water tank. The explorer inside did not seem to care that this rapid ascent would cost him his life. After rushing to the surface, the explorer had gone mad. The hatch opened, and he screamed and shouted in the sun, as if he was desperately trying to describe something terrible to us. After a lot of incomprehensible and confusing words, he uttered the only sober words:

“We all died there.”