Marinia stared into the abyss, clutched her satchel tightly against her chest, and wondered - not for the first time - whether she had gone mad.
Little light could penetrate this far beneath the ocean, and all that shielded the lonely seapony from total blindness was the pale glowing gemstone she wore around her neck. Before her, the reef's edge spilled away into darkness, the ocean floor plunging into a fissure of indescribable size. The tiny ledge highlighted by her light was but a sliver of the reality she faced; the Sephonic Trench stretched across the ocean floor for uncounted miles. Nopony had ever even speculated on its depth. To most it was just a mild curiosity on ratty old charts, unreasonably far from anywhere or anything of interest. Indeed her journey thus far had been a slow, solitary affair, with little to show for her effort but sore muscles and a pack of supplies far lighter than the one she'd set off with.
Time is sometimes unkind to the keeping of history, and things that were once well known often fade into the vagary of myth and hearsay. Tales that the hippogriff kings of ancient times once communed with the beings of the deep sea and learned of the Sephonic Trench - the so-called Hole in the World - were consigned to dusty storybooks in the corners of ancient libraries, now abandoned and no doubt looted bare. Nobody but a lunatic - nobody but her - would ever have believed that they might refer to something real. At least that's what they told her.
But now that her people had been driven quite literally beneath the waves, what was she to do? Mope around at home and drown in the depression of the hopelessly displaced? Or worse - frolic underwater like nothing had ever changed, like the queen? Inconceivable. Disrespectful in the extreme. Disgusting. She shivered with anger at the thought.
She would go further than any hippogriff or seapony had gone before in the name of discovery. Her work would demand attention and everyone would pay it. Her life would be meaningful again. People would care.
In the year or so since the hippogriffs had taken to the water, only Marinia herself had ever ventured this far from Seaquestria in person. Resentment, longing and fevered ambition flared in her mind at the thought and she carefully undid the satchel. Nestled amongst the meagre provisions that had sustained her far beyond the borders of the seaquestrian realm was a large, finely-wrapped package. And within that...
Untying the wrapping carefully with her teeth, Mariana was quickly rewarded by a glint of silver. Or was it silver? Though clearly metallic, the object was like no metal she had ever seen. It glimmered in her little light, the surface seeming to shift and glisten as if viewed through a layer of shallow water. Shouldering the satchel, she unwrapped her prize completely and regarded it with a scholar's eye. The wrapping, unheeded, drifted down into the black.
She held a tiara or crown of sorts. A strange piece of craftwork like nothing any living being had ever made. Its bizarre composition was matched by its equally bizarre shape - tall at the front, ascending to an array of fine points before tapering back and around with delicate, deliberate grace. Its face had been shaped and engraved with immaculate skill, but the designs defied her understanding. Geometric shapes, odd swirls that vaguely resembled sea creatures but could just as easily have represented clouds or waves. At the centre, a series of interlocking diamond shapes that shone like gems despite being wrought from the same material as the rest. Nopony alive knew of the trinket's history or origin, only its function and the fact that it had been property of the hippogriff royal family for many, many centuries. An heirloom fit for royalty, which she was not, but more importantly an object of great magical power.
Marinia smiled sardonically. Novo had always had a habit for collecting such things and hoarding them away where they were useless.
All that Marinia cared for now, though, was that this object - the Diadem Differentia - would allow her to push the absolute boundary of the known world. With shaking fins she placed it snugly upon her head, and in an instant she felt completely, utterly and inexplicably free. The weight of the ocean's water - untold trillions of tons of it - meant nothing to her. The artefact's magic guarded its wearer from the ravages of water or air pressure, great or small. Her eyes turned back to the Trench and its crushing depths and she grinned triumphantly; all of a sudden that great opening seemed to draw her, as if a door had been opened to a welcoming hall. As if a terrifying obstacle had simply swung out of her way, and a thousand mysteries beckoned for her - and her alone - to solve them.
With a flick of her tail she oriented herself straight down and began to swim. Down and down towards the foundations of the world, a tiny creature in a feeble bubble of light. With the cliff wall as her guide she made rough mental notes of just how far she had gone beneath the ocean floor. Tens, then hundreds of metres; the Trench was a vast gouge in the body of the planet.
As Mariana swam, deeper and deeper, the water rapidly grew colder. The chill of the deep ocean gave way to something worse; a stifling, near-freezing miasma that could only exist in the utter absence of sunlight. With fins pressed tightly to her sides she pressed on, her delphine body slipping through the water's frigid grip.
The water darkened around her as she plunged, chasm walls snuffing what faint, brave fragments of sunlight made it this far down. The far side of the trench swiftly disappeared from view, leaving only the near face by which to orient herself. Travelling directly downwards with her underside to the sheer rock, it was almost as if she were swimming along a new seafloor, rendered alien by the absolute black above.
Her efforts were not without reward, however. As she travelled she soon began to encounter signs of life - chalky, fibrous plants clung to the trench wall, attended by pale, eyeless fish. Bioluminescent invertebrates dotted the near darkness, creatures unheard of in any textbook she had read. Each new find delighted Marinia, vindicated her, and she paused in her descent to document them, making extensive notes both written and mental. Hours of work blended effortlessly together, and in cataloguing the mysteries of the sea she found herself in her element. She hadn't smiled this much since she had still been a hippogriff.
But even so, documenting minor flora was not the goal of her quest. The bottom of the Sephonic Trench still beckoned, and so each small detour was just that - a detour from the never-changing mission of down, always down. Before long the minor curiosities that lingered on and around the sheer stone passed into her wake, and the vertical landscape became jagged and barren.
Descending still she felt, rather than saw, shuddering motions in the deep. Unfamiliar creatures distorted the water with aching vibrations, at times threatening to scud her against the rocks - or worse, to drag her into the dark. She passed amongst unseen things that loomed like galleons and moved like magma with all the swiftness and steadiness her tail could manage. Points of light flickered and faded, vague and colourful in the distant dark. Muted, onerous sounds drifted mournfully from all directions - to her ears a bassy, burbling imitation of whalesong. Once she thought she caught the smell of blood in the water, thicker and oilier than it should have been, and swam swiftly onwards in case her clamorous instincts were correct. Was that a flash of teeth, or just her eyes playing tricks on her after relying on just the glow of her gemstone for so long?
Nothing interrupted her passage, however. Her sheer diminutiveness made her irrelevant here. She wished for a moment that she could stop and document the things just beyond her vision, that might or might not have regarded her tiny light with curious eyes, but that would mean venturing away from the increasingly sheer and barren trench wall - her one anchor of perspective. More than once she paused, taking the shortest possible breaks to rest, eat and fitfully sleep, quietly thankful for the fact that her stolen prize fit so snugly upon her head. The crushing weight of the ocean would claim her swiftly and brutally were she ever to take it off. More than once, she grappled with the thought of returning home. But every time, obsession won out over curiosity and caution; with the diadem freeing her from all constraints of depth, her mind was set on discovering the trench's very terminus. She clutched the tiny light strung around her neck and took a slow, difficult breath so cold that she could feel her throat turning raw.
Still she swam, ever further, into an endless fluid darkness.
With a start, Marinia realised that she'd lost track of time. In fact, she even couldn't be sure if she'd been swimming in a straight line. Her satchel of food and travel supplies was all but empty now, after days of descent. Fighting off a shudder of hesitation, she steeled herself and continued swimming. She had come here to find the bottom - the hidden secrets of the Hole in the World - and only cowardice could stop her now. Down and down, into unthinkable depths. Minute after minute, metre after metre flowed by in icy silence. She'd find the bottom. Learn the truth. Prove herself beyond all sane doubt-
And then, with a suddenness that took her completely off guard, the wall of the trench fell away from her. Marinia found herself without a point of reference, drifting and twisting and tumbling through the- water?
No, there was no water here; her fins beat spastically at nothing. Neither water nor air; she tried to steady her breath, but nothing entered her lungs. She was alone, adrift, in a lightless and silent expanse. Panic set in - perhaps the Trench truly was a hole in the world? Perhaps the sea continued downwards, forever, until it became something that was not a sea? Had her ambition led her to a place where nothing at all could live? Had she sealed her own fate in her thirst for knowledge, doomed to die alone where nopony would ever find her or even think to look?
And then, uncoiling, she saw it and froze. Far beneath her - insofar as 'beneath' meant anything - something moved. Something vast and slow. Faint glows manifesting into colours that burned her eyes, motion on scales incomprehensible. Impossible. Patterns and chaos, crags and great fields that flowed like water, rolled like tumbling rock, flexed and pulsed like living flesh. Circles within circles within circles, kilometres wide, beyond counting. The seapony froze in terror, uncomprehending, microscopic in the face of what she'd stumbled upon.
Her body, rigid beyond fear, tumbled helplessly in place. What had she found? What had she given her life to see? A sea monster? A living island? The very heart of the world? Her mind hurt to even put what she beheld into meaningful words. She knew the very act was futile - only the barest sliver of the thing was even visible - but to do otherwise was unthinkable. Somehow she knew that giving up on comprehension of what she had discovered would mean surrender to the bleakest form of insanity, to emptiness and a pointless death.
Thoughts not her own itched at the corners of her mind. Curiosity, confusion, interest, eagerness, caution. An unnatural warmth surrounded her - vast ephemeral tendrils rose sluggishly from the black and clasped her in a titan's grip.
Vision blurring, lungs burning, Marinia opened her mouth - to plead, or perhaps just to scream. And as she did so, the shining crystal about her neck flickered-
-and went dark.
