There was a movie Leo had seen when he was young. The theme was about a prison break, and he remembered that the film was based on a true story. It was about three prisoners who had successfully escaped from a heavily secure prison and were never arrested for decades. Since they still hadn't been caught, there was even talk that the escapees were still alive, though well into their 90s.
"Criminals can do it, so why can't I?" Leo thought.
Even though he was a model citizen who couldn't live a day without the law and had no experience escaping, Leo was confident there was nothing he couldn't do with Iris's knowledge as an 8th Circle Great Wizard and his own sharp wits.
"First of all, the only entrance is that giant stone gate, right?" Leo asked.
"Yes... As far as I know, that's the only way," Iris replied.
This place was clearly a stranded zone. There were no other prisoners, no guards, and no CCTVs. The only thing that had separated Iris from freedom for the past 200 years was the massive stone gate.
"If I just open that gate," Leo thought to himself, "I can tour a fantasy world full of mystery and adventure right away. But before that, I need to solve the barrier set up by a quasi-godly being."
"Iris, what do you need to open that door?" Leo asked her.
Iris hesitated for a moment before finally opening her mouth.
"...A holy relic? If I had a holy relic specialized in the world, I could open it right away," she said.
"...Anything else?"
"Well, well...?"
Iris's suggestion of needing a holy relic sounded as daunting to Leo as a father glancing at his emergency savings account when his daughter begged him to buy her a car. He imagined her insistence, and the moment when, unable to resist, the father would finally cave.
Leo thought to himself, 'A holy relic? No, the Mini Cooper would have been better. This was a private jet worth billions in magical value.'
"There are so many things needed to replace the holy relic," Iris continued. "All of them are difficult to obtain, and even if I could obtain them, it would be another problem to lift the barrier in such a short time."
"Any other possibilities?"
"Yes," Iris explained, "to put it simply, a barrier is a prison that is not restricted by its form. It's a prison that allows the sorcerer to confine whoever they want, with any restrictions they want, in any space they want."
"...Isn't that too much of a scam?" Leo muttered, feeling exasperated.
Although he had always been interested in magic, Leo had considered it a minor genre even among the many fantastical elements he had encountered.
"Magic is truly equal," Iris said. "Power comes with limitations. For realms that have been achieved through talent and effort over a long period of time, it offers a very high return. But for those who have not yet reached the realm, there are many restrictions that make powerful magic difficult to use."
Iris bent down and picked up a small piece of stone from the floor.
"There are three things needed to use barrier magic," she explained. She placed the small stone she had picked up on top of a larger piece of debris from the ruins.
"The first is the core that will be the center of the barrier," Iris continued.
She then picked up another fragment and scratched a circle around the core.
"The second is the spell that will become the barrier itself, which includes the restrictions placed inside the barrier as well as the wall that supports it outside the barrier."
Iris placed the stone fragment neatly within the circle.
"Lastly," she said, "there's the sacrifice. This is what helps those who have not yet reached the necessary realm to use a powerful barrier."
"Barrier magic is something that allows someone to temporarily reach a realm they have not attained, using a core and a sacrifice?" Leo asked.
"That's correct," Iris confirmed with a faint smile. "Sacrifices aren't limited to objects. Just as it's possible to substitute massive magical power for sacrifices, the same applies here. The World Tree's massive magical power serves as the sacrificial force maintaining this barrier."
"Then what are the core and spell of this barrier?" Leo inquired.
"That much... I don't know much about it..." Iris admitted, her expression tinged with frustration. "I've researched it myself, but all I've been able to decipher is the spell engraved on the outside of the barrier, on the wall."
She touched the boundary of the wall surrounding the stone sculpture with her hand.
"Originally, it's easier and simpler to identify the spell from inside the barrier than outside. As I explained earlier, a barrier is ultimately magic meant to confine and restrict. Just like how the gravity inside a barrier can be stronger than outside, you would notice it without anyone having to tell you."
"Uh... Then why can't you figure it out now?" Leo asked.
"This is just a hypothesis," Iris replied thoughtfully. "Perhaps it's because the restrictions within the barrier aren't directed at us."
Magic, Iris explained, targets all things in the world. If the restrictions of the barrier were specifically targeting the inanimate objects inside, the situation would have been much more complicated.
"If this was originally a prison, the restrictions would have suppressed the prisoners... but I don't know what this place was used for in the past," Iris confessed.
The cavern beneath the World Tree stretched out before them, vast enough to fit two or three soccer fields and as tall as the Empire State Building. Any sound louder than a whisper echoed off the stone walls.
Despite its massive size, there was no lighting anywhere. A large lake glistened in the center, surrounded by the scattered remains of ancient ruins.
"What on earth was this place made for?" Leo wondered aloud. "There's no way a cavern this size formed naturally. And even if it did, what's with all the ruins scattered everywhere?"
"Do you really have no idea?" he asked Iris.
"Yes... All I know is that the letters on the ruins are in ancient Elvish," she replied. "The language was used approximately 5,000 years ago..."
"5,000 years?" Leo echoed in disbelief. "Even Sumer, humanity's earliest known civilization, only dates back to around 4,500 B.C. The idea that there are records from over 5,000 years ago is incredible."
"Even for elves who live a long time, 5,000 years is significant," Iris added.
Leo took a deep breath. "Alright, so what's the plan to break this barrier?"
Iris gestured to a phrase carved into the stone near the gate. "'Blockade.' It's a simple spell, but incredibly powerful. It blocks everything from entering or exiting. Even if I used all my magic, it would still be a long way from breaking this gate."
Leo glanced at his phone, where a notification blinked on the screen: Would you like to return?
Quickly, he shoved it back into his pocket as Iris's voice trembled slightly.
"Um, Leo?" she asked.
"Yes?"
"If it's okay with you... wouldn't you like to learn magic from me?"
Leo blinked in confusion. "...?"