The mountain was one that rose with a gentle slope, contrary to the harsh environment existing in the frozen lands. It was low to be called a mountain, yet high to be called a hill.

  "Now we just need to find the entrance."

  Eren exhaled and grinned.

  "Right... do you have a plan?"

  Ari asked.

  "As the old saying goes, the fastest way is the most ignorant way."

  Saying that, Eren turned his body this way and that on the spot, intending to warm himself up. He looked ready to walk around the entire mountain. At Eren's words, Ari made an absurd face, took out the map, and pointed to a spot.

  "You're overlooking something important. The old man's testimony."

  At Ari's words, Eren tilted his head. The old man's words were so simple that they barely identified the terrain, but Ari had found something else in them.

  "He said he avoided the wind back then. I looked up the climate information for this area. At the time the old man mentioned, strong westerlies were blowing here. That means we only need to look at the eastern slope. And since there was no testimony about climbing the mountain, we should look for a terrain formed of cliffs around the eastern quadrant."

  Eren hugged Ari tightly and shouted.

  "You are my wizard!"

  Ari was flustered by Eren's sudden action. She carefully released Eren's arms, gauged the direction by looking at the sun, and then started walking slowly.

  After circling about half the mountain, a cliff terrain indeed appeared. However, the cave was nowhere to be seen. Seeing Ari disappointed, Eren grinned and said a word.

  "If human reason were always right, we would have predicted and avoided the severance of civilization."

  Eren looked around, put his backpack down in a corner, and rummaged for something.

  "Sometimes, crazy acts are necessary for progress."

  Ari tilted her head at Eren's incomprehensible words.

  Eren took out a stick-shaped explosive from his pack. It was prepared for rock blasting just in case. He took it and trudged toward the cliff. Then he buried it deep in the snow, turned his head, and grinned sheepishly. He looked like a child playing with fire. However, his hand was trembling minutely, and holding a flint in his other hand, he took a deep breath.

  Ari momentarily wondered if Eren had lost his mind out of disappointment. But soon she was convinced he was truly crazy. Eren was lighting the fuse of the explosive.

  "Run!!!"

  Before Ari could say anything, Eren turned and shouted as he ran.

  Ari cursed inwardly and ran in the direction Eren was running. She didn't know what on earth he was doing, but it wasn't the situation to argue. Eren passed her with a bright smile. And shouted back.

  "20 seconds left!"

  "Eren!!!!"

  Ari screamed.

  "19... 18... 17...."

  Eren ignored her cry and counted the numbers loudly. Ari threw off her pack without thinking further and ran. Just as Ari discovered the rock Eren was hiding behind and threw herself behind it.

  At that moment,

  "Bang!"

  Ari squeezed her eyes shut, pressing her body against the rock.

  The air folded in for an instant, and the next moment, it roughly pushed her back. Her ears went muffled as if they would burst, and all sound was torn away as if the world were submerged underwater.

  Snow and ice poured down like rain. The sound of collapsing was as massive as the amount of falling snow and ice. Soon, her ears could no longer accept sound. Tremendous vibrations resonated through her internal organs. And soon, heavy chunks flew around, hitting and breaking things. Shards scratched her face and hands, but she didn't even have a moment to feel the cold.

  Ari inhaled.

  No air came in. Her chest burned. She tried to scream, but no sound came out; instead, only a scratching vibration rang inside her throat. She instinctively hugged the rock tighter. Her body, lying prone on the snow, trembled, but she couldn't distinguish if it was because of the cold or fear.

  A moment later—a very short moment later.

  Sound began to return to the world. A sound like scratching metal rang in her ears from a distance, and over it, dull collapsing sounds overlapped. The fact that something was still collapsing was more terrifying than the loud noise ringing in her ears.

  "E... ren...?"

  Ari realized for the first time that her voice could crack like this. There was no answer.

  When she opened her eyes, her vision was entirely white. The blizzard reflected by the sunlight had not yet settled. She wiped her face with her hand and raised her body. Fortunately, her limbs were attached. She had sensation too. She was alive.

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  Then, a shape wriggled beyond the blizzard.

  "Hey."

  It was a familiar voice. It was so nonchalant that anger surged for a moment.

  "If you're alive, say something."

  It was Eren. Covered in snow and ice, he was lying next to the rock, coughing. White frost had settled on his hair, and red blood flowed from a tear on one side of his smiling forehead.

  As soon as Ari saw him, her legs gave way. Anger, relief, and fear rushed in all at once.

  "Crazy... truly crazy...."

  Eren shrugged.

  "But it opened."

  Ari looked behind him.

  Between the collapsed piles of snow, a darkness that clearly hadn't been there yesterday was gaping open. A cross-section of artificially cut granite. From inside, a very faint but distinct warm current was flowing out.

  Ari looked at that darkness and swallowed.

  "...It's really there."

  Eren didn't smile. Instead, he took a deep breath for the first time.

  "I told you."

  His voice was trembling slightly.

  "Sometimes... crazy acts are necessary. Haa... haa... And you know... I trust you, Ari. And I thought you couldn't be wrong."

  Eren grinned. The two caught their breath behind the rock, listening for signs of additional collapse.

  Around the time the ice fog blocking their view subsided, Eren stood up first. He looked around carefully to see if anything else would break or collapse. Then he took a hammer from the backpack he had thrown in the corner and tapped here and there to check safety.

  Ari brushed the snow off her clothes, stood up, and trudged over.

  "You also overlooked one of the old man's testimonies. That the cave was warm. That wasn't simply because it avoided the wind. It was actually warm. I figured even if the entrance was blocked by snow and ice for ten years, the entrance side wouldn't have completely frozen."

  Eren said as Ari approached. At his words, Ari scoffed and asked.

  "Then what about your confidence that the amount of explosives was appropriate?"

  "That... I just felt it would be...."

  Ultimately, Ari realized Eren had made a gamble that nearly buried them alive, and she was dumbfounded.

  "But it opened."

  Eren politely extended both hands to guide Ari to the entrance, like a servant escorting a noble.

  Entering the cave, Eren took a prefabricated oil lantern out of his backpack. Meanwhile, Ari quietly examined the surroundings. The cave was about twice the height of their medium stature, and it was an arched shape with surfaces so well-polished that it was noticeably artificial at a glance. Ari touched the surface and said.

  "It's granite...."

  At Ari's words, Eren couldn't speak. He had some knowledge of geology from excavations, but this was the first time he had seen a granite structure of this form.

  "This was literally carved. Such a massive structure... the technology of the ancients is truly amazing."

  Ari admired it again.

  "Furthermore, warmth is coming from somewhere... is magma flowing underneath?"

  At Eren's question, Ari shook her head.

  "This is granite. That means magma flowed hundreds of millions of years ago. Furthermore, if this were a lava zone, the surroundings would be affected, and there should be geysers or at least traces of water flow. As you know, there's nothing but ice and snow around here. This warmth is artificial."

  At Ari's words, Eren's eyes shone.

  "Something emitting heat for over ten thousand years?"

  "Or it was activated recently...."

  Ari assumed all possibilities, but no matter what assumption she made, the fact remained that it was a functioning ruin that had withstood a tremendous amount of time. Ruins were literally ruins. Remaining traces and dead things. Not living things. So only by picking up pieces, fitting them together, and patching the empty spots did they barely become meaningful. But even that was only possible with the support of modern human knowledge. Some ruins had operating principles that couldn't even be guessed, and some items had unknown power sources. Even some documents made one wonder if they were a collection of symbols rather than a language.

  But what if it actually worked?

  Its value was incalculable. Eren also realized the meaning. Unable to hide his excitement, he shouted to Ari.

  "We're rich now... and you'll be a hero of the artifact excavation academia!!!"

  Ari, who received a lantern, quietly looked around for clues about this place. Eren led Ari, suggesting they follow the traces of warmth. This massive cave structure was deep enough that its scale couldn't be known, and as they went deeper, it widened to the point where they wondered how it was made.

  "This must have been an underground structure."

  Ari said, recording the number of steps they had carefully walked and the directions they turned in between.

  "Is it like the treasure warehouses and mazes in legends?"

  Eren asked in a slightly excited voice. Ari rebuked Eren's joke-like words.

  "Those are just stories for putting kids to bed. Record it well if you don't want to become a ghost who died wandering in a maze."

  While Ari drew the map, Eren walked a few steps ahead and said.

  "Ari, I think you're right. This is uplifted. Though I think it's due to the cold."

  Ari continued.

  "Judging by the shape of the path, we didn't enter through the main entrance. It seems we entered through an intermediate passage exposed as the ground uplifted."

  Ari shone her lantern back and forth. Endless passages were pierced here and there.

  "Let's go up. There might be more information about this place."

  Ari called Eren, who was going in the opposite direction.

  "Why?"

  "You said it. People think similarly, whether ancient or now. Where is the place name usually located?"

  Eren quickly came up with the answer to Ari's riddle-like question.

  "The entrance?"

  "I think you're more suited to being a fortune teller than an excavator."

  Eren chuckled at Ari's silly joke.

  "But is the place name more important than treasure? What's the reason for going to the entrance?"

  "Items sell better with a story. Plus, if we know the place, it's easier to know what the artifacts were for."

  Ari left those words and walked with long strides.

  After walking for a while, Ari stopped quietly in front of a wall. There were letters there. She didn't know how old they were, but perhaps because they had avoided the weathering inside the granite cave, the letters remained clear. Ari brushed the dust off the frozen surface with trembling hands. Regular engraved traces were felt under her rough gloves.

  "Can you read it?"

  Eren asked with a trembling voice, bringing the torch closer.

  Ari hurriedly took out the ancient language dictionary from her pack and compared it. Her eyes moved quickly, but soon her brow furrowed.

  "Damn it... this isn't an ancient language I know."

  "What do you mean? You said it was an ancient civilization?"

  "The grammar is too different. This... isn't everyday language. It's like a highly technical dialect or a code used only by a specific class. Or the era is completely different...."

  Ari's fingertips stopped on the largest and most boldly carved word at the top of the sentences.

  "No, wait."

  Ari closed the dictionary and slowly traced the letters with her finger. The only simple combination amidst complex grammar. A proper noun whose pronunciation could be inferred even after enduring thousands of years of linguistic weathering.

  "I can read this. It's not a technical term. It looks like a place name, probably the name of this place."

  She slowly traced the first word with her finger. Examining the characters before her closely, she substituted similar pronunciations recorded in the dictionary. She swallowed hard and read aloud the name left by humanity tens of thousands of years ago.

  O – N – K – A – L – O

  "...On...ka...lo...."

  "Onkalo?"

  Eren asked back.

  "Yes. It's definitely the name of this ruin."

  A confident smile spread across Ari's face. Ari flipped through the dictionary again.

  "It seems to be a compound word in the ancient language... combining within what I know, it's similar to 'hidden place' or 'hollowed place'. It probably means something like that."

  At Ari's words, Eren became even more excited.

  "Think about it, Ari. Isn't that the most fitting name for when kings hide treasure? Onkalo. We've come to the city of gold... Ari."

  At Eren's words, Ari nodded.