With a good leap Pine Scent easily cleared the tumbling stream, Well, tumbling was something of an understatement. It was really more a seemingly endless series of cascades ranging in height from no greater than a single stair step, up to taller than a two story house. Landing on the other side with the sharp clop of hooves on granite, Pine paused briefly to check that her thick diaper was still firmly in place after the hard impact. Heavy as it was with her pee, and a squishy mess, she was worried, perhaps unnecessarily, that the tapes might not hold. Having assured herself that the diaper was just as snug on her as it had been all morning she wound her way up the heavily worn, carved steps leading up to the rectangular stone entrance to the passage, itself leading back into the canyon wall. Brushing by hardy stands of Flamebush who’s leaves were now at the prime of their namesake color due to the oncoming autumn season, she reached and then passed through the now cleaned out passage entrance into a much darker realm. Her hoofsteps sounded loud in her ears as their noise reflected off the hard stone of the surrounding walls. As a testament to the age of the place, noticeable cracks ran across the floor and ceiling of the passage showing just how much time had passed since the tunnel had been carved out. Many millennia must have come and gone to allow the rock of this area enough time to shift enough to form cracks of noticeable width.
As the passage bent slowly to the left the sunlight coming in from the entrance dimmed down to nearly nothing. Pine set the tip of her horn aglow as she continued along. Almost immediately the mixed piles of stone, sand, and tree branches that were washed in whenever the stream flooded began to thin out. This marked the furthest extent of her progress from the previous day when she had first found this site at the far end of her cousin’s property thanks to a tip from her older sister. However, as she climbed over the last of the debris piles she could see around a bend in the passage to where the roof had partially collapsed and the pile of dusty tan stone ended just feet below the ceiling. It looked like she could simply duck under the hole that had been left near the top of the pile and look into what she hoped was a continuation of the passage unless there were further interruptions. She wondered how much excavating would be required if anyplace had fully caved in beyond this particular obstruction. Assuming of course, that this passage went anywhere at all.
As it was still early in the morning she wondered how long it would be before anypony else from back at the house would realize she had left on her daily adventure and if something were to happen in here, how long it would be before they found her. Would they ever? The thought made her shudder a bit.
She promised herself that she wouldn’t go in too far, and that if anything seemed too dangerous she would simply turn around and leave. Besides, she didn’t want to go crawling over sharp rocks or through tight holes simply in the name of curiosity while she was wearing her diaper, and such a nice one at that.
She had been, so far as she knew, the only one of her family to have gone to sleep early last night and so get up just as the sun had been rising over the surrounding misty forested hills, the sunlight glinting off the struts of the fire watchtower several kilometers distant. To get to the stream where the hidden ruins of the tunnel entrance was located had required an hour and a half of hiking past the watchtower along a sometimes quite poor excuse for a trail. Between the amount of time she had as a head start simply by getting up so early and the amount of time it took her to walk all this way, she probably had a few hours to herself here at an absolute minimum, and to be realistic probably all day, before any of her siblings thought to come this way to look for her. She wasn’t the only pony in the world who knew this place existed after all. But one way or another she was certain to get plenty of time to enjoy more walking and running and exploring with her heavily used diaper squishing about between her legs and making her feel… sensitive. She always had enjoyed being regarded as the up-at-the crack-of-dawn one and being able to routinely do so gave her lots of time to herself in the mornings.
As she made her way up to where the piles of rock choking the passage connected with the celling she became aware of the faint sound of blowing air. It wasn’t coming from behind her where she would expect it to be due to the entrance lying in that direction but from ahead. If fact, it seemed to be strongest at the top of the debris slope and blowing past her towards the mound of rock, as thought the passage was somehow inhaling. As she scrambled up the last of the mass of rocks and sand the sound became more distinct until she found herself staring at the top of the pile and at a group of small dark holes between the rocks. The faint green glow from her horn did little to illuminate where the holes went or even much of her surroundings for that matter but the rushing air must be going somewhere.
It occurred to Pine suddenly that she had encountered a similar phenomenon before in a natural cave system near the eastern edge of the Everfree Forest. Whenever a weather front moved across the area the outside air pressure changed, causing the cave system to either expel air if the pressure outside decreased or to draw in air when the outside pressure increased in a constant hunt for equilibrium. As the cold front had passed by the previous day they were now under a one of higher atmospheric pressure. And sure enough the air was being drawn, or more appropriately, forced into the tiny passages. This excited Pine Scent greatly because not only did it mean that there must not be any cave-ins of the passage that could block air flow, but also that the passage way must lead to either a very large chamber or a very extensive network of other passages for there to be enough volume to create such a forceful draw of air.
Pine began to push on the sand and stones surrounding the black suction holes and watched with glee as it all disappeared into the little pockets of blackness and presumably on to whatever was on the other side. After all, when nature provides a vacuum cleaner a pony would be stupid to not use it. After a good half hour of this process Pine had transformed the collection of several small holes into a single large one, just large enough to perhaps scramble through. Every time she touched the sand and loose gravel around the edges of the hole it was as if a small explosion was set off as a cloud of bits of dry stone and sand was greedily pulled through. Pine estimated that the air was probably being sucked in at a rate of at least eighty kilometers per hour if not more. It was actually quite loud at this point and she was sure it could be heard some desistance off. She couldn’t help grimace at the thought that if anything did inhabit the passageway beyond, it would probably know something was going on near the entrance by this point.
Finally deciding that she couldn’t bear the anticipation of discovery any longer, Pine took a deep breath and pused hard on the rocks at the top of the wider hole as hard as she could. There was a grating sound as they shifted and then a section of the slope near the celling collapsed to fill the whole she had been stuffing bits of rock into, groaned some more, and half fell, half sank backwards and out of sight causing a rumbling and crashing as a cascade of a dozen rocks larger than her head went tumbling down the far slope.
She shut her eyes tightly against the blowing dust and stooped through into the now nearly pony sized hole with its much reduced winds. Immediately her mane was being whipped around over her face. She made sure to be extra cautions taking the next few steps as the rocks were loose and it would do nopony any good if she went tumbling down the far slope, diaper and all, in the same fashion as the recently dislodged rocks. She was also careful to face downward so that her horn would point straight out and not scratch along the ceiling. Even though the outer surface of a unicorn’s horn is mostly composed of the same substance as tooth enamel and quite hard, the sensation would nonetheless be very unpleasant.
Even though Pine had been dimly able to tell what lay beyond the newly opened stoop-way she had just gone through, she really had no better idea now she was on the far side of the cave-in. Only by peering into the darkness and making her horn glow as bright as she could get it was any further detail reveled to her. Helpful knowledge to have before plunging muzzle first into the unknown.
She opened her eyes as quickly as she thought she could get away with and was swiftly proved wrong when dust got in forcing her to close her eyes again as they began to water in an effort to remove the grit. Shaking her head in annoyance at the discomfort and having to yet again have to take some more cautious steps down the slope of loose rock in order to get further from the dusty wind, Pine made more of the decent anyway out of sheer determination. Rapidly blinking the remaining irritants from her eyes and peered about herself. She was now almost back down to the passage floor, with only a few more feet of sand between her hooves and the smooth stone. As she turned back to look up at where she had come from she thought she could tell why the passage had been blocked up to this point and no further.
There seemed to be the remnants of a metal gate sticking out from the accumulated sand in places. It was composed of metal bars as big around as her legs which crossed each other at ninety degree angels to form a grate of hundreds of square openings. At least they had all been square originally. The grate was now mangled and warped. The hole near the ceiling she had come through happened to pass near the corner of the passage where the grate had been mashed into itself forming an opening. What had probably happened at first was that flood waters had brought in all manner of branches, roots, twigs, and whole bushes which had piled up against the framework of metal bars and before rotting away over centuries had allowed sediment to back up behind them. Once formed the sediment pile had only continued to grow. She decided that in truth there never had been an actual cave-in this location. Instead it was simply a large rocky version of a log jam in a river. Turning forward Pine quickly became distracted from the oddity of the old mashed gate of metal bars by the beckoning call of the unexplored.
Pine had not gone far before the corridor she had been following and that turned constantly but nearly imperceptibly to the left ended in a flight of several dozen stone steps and opened up into a wide rectangular chamber. As she crested the rise of stairs the glow of her horn was lost in the blackness above, meaning that the ceiling of the chamber must be at least fifty meters high. Odd that a room would be taller than its length in any other dimension she thought, but then nothing about what she was exploring could be seen as normal. Suddenly something on the righthoof wall caught her eye. It was a relief carving. The first sign of any ornamentation she had yet found in this place. As she walked nearer to it she realized just how impressive it was. It was not so great in size, only measuring around five meters high by two meters in width, but the lines and shapes that were carved into the stone had been done so with spectacular precision. At first she was not quite sure what she was looking at but eventually she came to the realization that she was being shown the perspective of being so high in the sky that she could see the roundness of the world, or at least a world. There were also other worlds in the image, one had what looked like a ring and another seemed to have many smaller worlds around it. The strangest thing of all was what appeared to be a sun in the middle of it all. How could that be possible when Celestia herself raised and lowered it every day? Surly the Sun must go about Equestria. Pine began to doubt that the work was supposed to present any realistic scene and may have been nothing more than an interesting interpretative piece even by thoes who had originally carved it.
Though even as she considered it, the possibility didn’t sit right with her. Why would a civilization go to all the work of crafting only a single work of art in a large chamber if it meant little more than decoration to them, especially when they, whoever ‘they’ were, had not seemed to be interested in decoration anywhere else she could find. No, it must have had some significance but she had no idea what it might be. Tracing her hoof along the sharply cut lines she almost felt like she had seen this work before, or at least something similar. But whatever it was she couldn’t quite make a connection. Shaking her head in confusion Pine turned away from the carving and headed along the otherwise featureless wall towards the far side of the chamber where she figured a continuation of the previous passage would exist if it did anywhere. Knowing how far she had walked from the entrance, Pine almost wished she had come out here with a member or two of her family. Even if that did mean she couldn’t now be enjoying the feeling of all the warm squishy mess and pee filing her diaper. Perhaps she really shouldn't go beyond this point even if she did find a passable way forwards.
As it turned out no obvious way deeper under Equestria was immediately apparent.
This was something of a disappointing turn of events pine thought, especially after the large amount of work that had gone into getting where she was now. However, she could hardly say the trip had been a failure, how long might it have been since anypony had seen this chamber? And maybe there was a way on. But this area was in the foothills of the Unicorn Range, which were the source of the oldest known centers of pony civilization, even if that period had been so racially divided that it hardly deserved to be called a civilization. Regardless, there were stories about nasty things that came from ancient ruins such as these and perhaps a single mare in a diaper was not in the best position to deal with anything ancient and magical.
She would return, she was sure of that, but perhaps next time it would at least be with her parents, and if she was lucky maybe somepony, an expert hopefully, from the capitol. With one last look around the rectangular hall, the oddly single relief carving on the wall and the celling so high it disappeared into the darkness above, Pine Scent turned herself around and headed out the way she had come, looking forward to seeing by real sunlight again instead of just by the dim glow of horn light.
Reaching the end of the tunnel and smelling the cool, fresh mixture of clear stream water and autumn leaves made Pine simply happy to be alive and able to be out here in nature and experience its beauty. Being able to do so with the comfort of her warm dirty diaper wrapped snugly between her legs and about her thighs and butt was just about the best she could hope for. Pine idly wondered how many other mares in Equestria enjoyed diapers as much as she did. Probably not many, but, well, who knew, what if one of the princesses did? Now there was a thought, and the image made her giggle a bit.
Finding a place where she could leap back over to the other side of the incessantly tumbling brook was the work of nearly five minutes, but she made it at a point where two large boulders happened to be positioned just right to jump from one to the other.
A further ten minutes past that was enough time for her to backtrack to gather up her small set of saddle bags which contained little more than a towel and various simple hygiene products, and then walk to a spot she had seen earlier from the stream’s other side where a very large flat rock tilted slightly into the stream. Most of it was overhung with several large pine trees, appropriate somehow, which provided good shade. It had been cool during the morning and in the underground tunnels, but now it was nearly noon and was near thirty degrees. Enough to be a bit too warm if one was sitting out in direct sun for long.
She spread her towel out on the clean rock surface only three meters from the froth of one of a hundred low waterfalls and with a sigh and a soft squish sat herself down. It was beyond her ability to resist sliding her butt back and forth a few times in the poop spread around the inside of her diaper. She must be quite a sight under the thick wet padding but she didn't care, the feeling was too enjoyable for such minor annoyances as a future mess to clean to be of any real bother. She simply sat there with a smile on her face. A hoof on the front of her diaper and another sigh, and she was wetting herself again. The urine’s warmth flowing down and around the insides of her diaper, following wherever it did. A bit more, well maybe more than just a bit, of sliding herself around in her tight but thick diaper and Pine Scent laid back on her towel with just her diaper and the rushing stream for company. It was going to be a long day, just the way she liked it.