After an intense fight with a formidable opponent, the Griffon became my very first tamed monster. To solve the mystery of the plains, me and my sister mounted the monster and soared throughout the entire plains.

We flew around the whole plains and grasped the entirety of it. The flight was around sonic speed and we covered the dimensions of the vicinity in short time.

"Based on our aerial investigation, the plains is in perfect circle and has a diameter of twenty kilometers."

"When I checked the soil earlier, the earth was not compacted and the plains is no barren. It looked man-made but it's definitely natural."

"The soil is not as fertile as the forest. It's like a piece of land from somewhere were dropped in the middle of the forest. But I'll reject that possibility for the land to slowly become fertile as the time pass."

"You're right, Sis."

After we survey the land midair, we took a rest under the shade of a small grove of maple trees within the plains. Cold winds touched our skins and blew the orange autumn leaves as the seasons transit.

For us to feel the breeze of the upcoming winter, I opened my Inventory and set up wooden table and chairs on our resting place. Prepare some ceramic plates and serve it with my piping hot homemade D-ranked Great Boar skewers. Though I grilled it years ago and keep it in my Inventory to maintain it freshness.

We need calories to fill the burned energies from our today's activities. I also cooked the amputated Scythe Mantis limb and it taste like crab.

(I'll cook the meat and sell or make a use of the blades and exoskeletons.)

Griffith, the name that I bestowed to the Griffon, also joined our meal and is currently chomping a C-ranked Cockatrice that I hunted years ago. I named it Griffith because it sounds like Griffon, Griffin, Gryphon, whatsoever.

But when Sister asked, 'Do you even know its gender?', it felt like a supernova suddenly exploded in my face. I checked its genitals and confirmed that male-named Griffith actually had no Y in its chromosomes.

(Her title says 'Sky Queen' itself. I'm so blind.)

While eating our rations, we discussed about our findings and speculations of this abnormal phenomenon. But we haven't concluded a single thing.

"This perfect circle piece of land is too unrealistic. The reason behind its formation is still a mystery. And there were less monsters appearing and not affected by the forest's thick mana and fertility."

"Yeah. Lesser mana doesn't make plants grew too much and contains not too much nutrients. Making it unappealing to plant-eating monsters. Even if one entered the plains, it will be hunted down by Griffith." I said as I placed the right side of my face on the table and continue, "You can only draw a perfect circle with a pair of compasses… A pair of compasses? That's it!"

"You got in mind?"

As we were seeking for answers, realizing how things made up, an idea came up in my head. I raised my head and grabbed the used metal skewers on my plate. Used Alchemy to mold it to a pair of compasses.

Thud.

I struck one of its arms on the wooden table and slowly rotate the metal, leaving inscription behind.

"A perfect circle was done by drawing a line with fixed distance from a given point."

"If there's a perfect circle, there's a point that revolves its radius. Since this plains is in perfect shape, it means that there's a center that make it round."

"If we pinpoint its center, we might find an answer, or at least clues, to explain this plains' irregularities." I declared as I complete the rotation of the compass, carving a perfect circle on the table.

We are now getting closer to put a dot to our investigation. If this only hint leads to nothing, we don't know what to do or where to start anymore. So I has high hopes for this one.

"That's decided then. Let's move out." Sister stood from her seat and approached Griffith, who's done eating her share.

I followed suit as I taking back the set to my Inventory. The sun is still blazing and it's about three o'clock in the afternoon. We have more than two hours before our five o'clock curfew.

"No matter how much I stroke her feathers, I can't get enough of it. So is so soft that I wanted to sleep on it."

"I, too, was captivated by that soft feathers. But you know that we cannot take her home, yes? Her presence only can freak out even veteran adventurers, how about common people?"

As I arrived at their position, Griffith laid her back on the grassy surface, exposing her pure white feathered upper torso. Sister wrapped her arms around Griffith's feathered chest with her knees on the ground.

Because of Griffith's intimidating appearance, we can't just bring her home like picking a stray cat. Her size and existence could attract the gazes of malicious people and started hunting Griffith for her valuable raw materials.

"I know, but can you do something about it?"

"I can change her size if I bestow her Size Change. But it's still inconvenient for having her continuously consume large amount of mana just to keep up her minimized size."

"What a shame… I wanted to keep her in bed…" she just mumbled something inaudible after my explanation.

"You wanted to know the truth behind this irregularity, right?"

"Yeah…"

"So get your well-endowed butt up to get Griffith stand."

As if following my words, Sister straighten her knees then Griffith rolled and stood up. I climbed on Griffon and laid my butt on her back. Sister follow suit and successfully mounted Griffith behind me.

For me to withstand inertia, I created an impromptu bridle just after I tamed the airline. I didn't made a saddle for Griffith's feathered back already comfortable.

With nothing to hold on, my sister wrapped her arms around me. I held the rein and ordered Griffith to soar into the sky.

"Hold tight, Sister. We're flying at the speed of sound."

After that, Griffith flapped her wings and burst at sonic speed towards the center of the plains. Just several seconds, we arrived at our destination without a hitch.

"There's nothing here. Just small hills and thickets."

"We might find something if we land."

Just as Sister suggested, I ordered Griffith to land near the center. Same as before, all we can see are grassy hills and trees. We even check the surroundings to find nothing.

"There's nothing at all."

"If not on the surface, how about underground?"

"I'll try."

I activated my Unique Skill Omnidirectional Perception and powered it to its maximum output. Enough to cover the entire area of the plains. I scanned every corner of the coverage and noticed something that was unlikely to happen.

"Hmm? What is this?"

"What is it, Raphael."

"For unknown reason, there's something that my Omnidirectional Perception could not detect. If I haven't maximized my skill, I wouldn't have found it."

"Do you know what is it?"

"I don't know, but it is definitely blocking my perception. It's flat and located around a kilometer beneath us. It's wide and vast. It's exactly as perfect and as big as this plains."

My Omnidirectional Perception can detect anything within my spherical range. But this is the first time I encountered a thing that my all-seeing cognition couldn't sense. Rendering a Unique Skill useless need at least to be at the same level or higher.

"Not just that, there's also an undetectable object buried under that hill." I said then pointed my index finger on a certain hill.

The hill is quite slopy and about fifteen meters tall. Covered with verdant grass and surrounded by trees. It's located exactly as the center of the plains.

"Level."

To make the object appear, I casted a Level 2 Earth Magic: Level to flatten the ground. If used by average magician, it's quite difficult and took long time to flatten a lump of earth of this quantity. Since I have lots of mana and magic power, I will be able to flatten this hill less than a minute.

As the hill slowly descends, the object started to manifest. Since it's undetectable, it was excluded from my spell and remained unwavered.

The hill continue to descend until it completely flattened out, leveling the vast plains. The he full image of the buried object finally unfold in front of our eyes.

"What is that? A door?"

"Yeah. No matter where I look, it's definitely a door, or a gate?"

The object that was buried under the hill was a large set of double doors. Standing at five meters high and is stretching around ten meters wide. Wide enough to be walked by several people abreast. The doors seems metallic and the twelve-inch thick cylindrical frame was somewhat made of pitch-black stone.

"Centuries or even thousands of years of being untouched, the soil piled and stack up until it covered the whole door."

"Looks like it. But why its looks familiar?"

"This stone… I can't detect it even when touched… and I think I have seen material this before…" I pondered, touching the frame.

"It looks like the city walls of the Imperial Capital… Now that I think about it, it's looks exactly the same door that I have seen in the same city."

"Indeed. Based on what we're gathered so far, this door is, without a doubt, an entrance to enter a dungeon."