A Wolf's Howl, A Fairy's Wing

With a disappointed sigh, Naeku nodded and stood up from his lap, quickly followed by Erik. With a snap of her fingers, she conjured her armour around her body and hid the incredibly sexy clothing Erik so preferred seeing her in. That said, she immediately transformed to werepanther form as well, so those clothes wouldn't have been interesting for much longer, anyway.

Hiding his regret, Erik elegantly waved at the door. "Ladies first," he smiled, and Naeku giggled.

In mere moments, they were walking down the hall, side by side.

"Have you tried using your nature sense to look under the ground before?" Erik asked, an eyebrow cocked.

"Only superficially," Naeku answered, brows creased. "I checked a few meters under the ground for basements and such, back when we first started living here. I found a few, but they were all clearly connected to ground-level buildings—I found nothing like what Elora tells me should be there."

"Well… No time like the present," Erik grinned, excited to find out what this city is still hiding.

Naeku nodded seriously. Immediately, green runes appeared around her eyes as she activated her nature sense. "I'll just start by diving deep…" she muttered, and did exactly that.

They continued walking as they did so, but it wasn't more than a second or two later, before Naeku halted in her steps with wide eyes. "Ah!"

Erik raised his eyebrows. "You found something already?"

He knew her nature sense was just as quick as omnisense, but he expected this to be a little harder.

"I… maybe?" she whispered, her brows creasing in confusion. "I've never experienced anything like this… The only impediment to my nature sense has always been range, but this… this is something I can't see through!"

She looked up at him with something akin to panic. "T— There's a massive, metal box, several tens of meters under the city! I— I can see through the metal, but then there's… there's something stopping me from going further! I— It's so empty, I—"

Her tone became increasingly frantic, and Erik quickly stepped forward with a frown. He wrapped his hands around her, and she was snapped out of it as she deactivated her nature sense.

Feeling her shiver a little, Erik grew increasingly concerned. "Are you alright…?"

After taking a few deep breaths with her face buried in Erik's chest, she eventually nodded. "Y— Yeah," she sighed, and stepped out of his arms, now looking embarrassed. "I'm… not sure what came over me, to be honest. It just felt so strange and alien, I…"

She shrugged, unable to find the right words. Erik immediately grew concerned about exactly what was beneath the city.

Fortunately, Elora was quick to offer answers. With a flash, she jumped out of Erik's dimension and appeared on his shoulder.

She could do this because, in preparation for today, Erik had closed the dimensional portal in the palace and turned himself into the portal again. He'd put the stationary portal back later but right, now he wanted his full capabilities at hand.

"It sounds like this was the first time you felt a vacuum," she said sagely, having already entered teacher mode. "They say a vacuum, or nothingness, is the antipathy of nature. It's well documented that anyone with an ability similar to your nature sense is… thrown off when their sense touches a vacuum for the first time."

Noticing the concerned emotions in Erik's mind, she smirked and shook her head. "Don't worry, it's harmless, just a little disorienting."

Erik looked relieved, but Naeku obviously remained a little haunted by the feeling of a vacuum.

Regardless, knowing there was no immediate danger, Erik cocked an eyebrow. "Alright, so there's a vacuum beneath the city? What does that mean? That room those three ended up in definitely wasn't airless."

Elora shook her head. "No, it wasn't. Although Naeku can see a large metal box, I'm sure it isn't all a vacuum inside. Rather, they've employed a well-known, but difficult, method to isolate a space as much as possible, using a combination of magic and natural principles."

Seeing Erik and Naeku were completely lost, Elora explained with a knowing smirk. Somehow, when these two didn't know something, she didn't mind, and even enjoyed explaining the principle, but when Ankhur or anyone else was clueless, she'd berate them.

"Let me put it this way," she began, "skills such as Naeku's nature sense hold so much power precisely because they aren't transmitted through aetherium, as omnisense is. Instead, they move directly through ordinary matter, gaseous or otherwise. That's why they're so hard to interrupt: you can block or interfere with aetherium-based omnisense, but you can't stop something from being made of physical matter."

She looked at Naeku with true appreciation for her ability. "That's why, to make absolutely sure no one can spy into a place, you need to make sure there's not a single bit of matter for one of these abilities to travel through—not even the molecules floating in air."

Realisation struck, as Erik and Naeku nodded at the same time. "So that's why a vacuum…" they both muttered.

Like a proud mother, Elora nodded. "Right! As I said, this is a well-known method, but one that's difficult to achieve. I suspect they've essentially created a smaller metal box, inside a bigger metal box, then used sigils to create an incredibly powerful, repulsive magnetic field inside the walls of the bigger metal box, thereby suspending the smaller metal box in mid-air."

Her admiration for these city builders was clear as she continued excitedly. "After that, all they had to do was turn the small empty space between the boxes into a vacuum. It's likely that there's only like a finger length of space between the two boxes, but that's more than enough to keep a skill like Naeku's nature sense at bay."

Both Erik and Naeku blinked as they stared at Elora in disbelief. Despite having had eight years to come to terms with the existence of magic, a construction like this was still unimaginable to them.

"All that effort just to defend from my nature sense…?" Naeku muttered softly, suddenly feeling quite proud of her ability.

"Hehe, well yeah," Elora giggled mysteriously. "Didn't Erik tell you how excited I was when we found you? Besides, there are plenty of sigils out there that can emulate something like your nature sense, so something like this is a basically a necessary effort if you have the means and want to keep something truly secure."

They took another moment to come to terms with this revelation, and then continued moving through the halls, deep in thought.

"So… Have we learned anything useful from this?" Erik eventually asked, an eyebrow cocked.

Elora shrugged. "Well… we know now that there's definitely no physical way of getting there, because that would defeat the point of creating a thing like this. So, what we're looking for is some kind of teleportation, much like that trio used to get in there…"