202 years ago:
The child had been walking for hours finally making it out of the city. She had been tired of being ignored by her parents. Two high level corporate CEO's who thought good parenting was seeing her a few hours on the weekend while talking on the phone dealing with business. Let's not even get into other children, she couldn't stand them, they were snotty and treated her poorly because she was so plain looking. She was definitely plain one those faces that just seemed one of the crowd; easily dismissed and forgotten.
So, she decided to make her parents focus on her by running away to the mountain for a few days. She wore a hideous striped sweater that her mother thought was all the rage. Snot green with shit brown stripes. She paused when heard the familiar warning sirens in the city go off. Another bomb drill she sighed before she kept going. She'd only gone a little way a few minutes at most when she heard a sound like an explosion in the distance.
Turning to see what it was her jaw dropped in horror as she saw the distinct mushroom cloud from an atomic bomb. Watching as parts of the city were engulfed in a raging inferno. Another sound that was far closer came behind her and before she could fully turn around bright light enveloped her for a moment. She didn't even get a chance to call out for her mommy before she was over came her body along with the rest of the surrounding area instantly vaporized. There was literally no one left alive on that day that knew of her or that she even existed. The child named Frisk was lost to history along with billions of other lives on that horrible fateful day.
Unknown to the world or more a forgotten tale that only ever mentioned in old fairytale books, the mountain held a secret a deep secret. It was the entrance to an underground world filled with non-human beings; hell, even none humanoid beings. The bombs didn't just kill off most the humans in the area but had leveled a good portion of the mountain.
There had been a cave with a huge hole in it with a shimmering film over it or perhaps the more accurate term would be to say that it had a barrier. A barrier that had been keeping the denizens of the underground world from coming to the surface for thousands of years.
Yet when the bombs leveled the mountain the barrier which was infinitely stronger on the inside than the outside collapsed and tons upon tons of rubble fell into and filled what was once the large gaping maw to the underground. It would take the denizens roughly 200 years before they managed to clear the rubble, thou at some cost to life due to the fact they had to dig upwards into unstable rocky ground.
2 years ago:
The last of the solidified rubble gave way in a precise and planned manner to minimize risk to the workers. Fresh air from the surface rushed in for the first time in 200 years. They were surprised they figured they had only gotten half way up the shaft. Concern filled those that oversaw the project as well as those working on it. A volunteer was sent up to see what the deal was as bright light poured into the shaft thou it was only bright in comparison to what they had been use to.
After an hour of careful climbing a large webbed hand gripped the side of the hole and pulled itself up. The figure that emerged could only be thought of as a monster from the old monster flicks that humans use to watch. Its skin was a motley earth brown and sea green and scaly. As it pulled itself all the way and stood up at only 3 feet of height it was clearly not human in the least.
Two large bulbous eyes seemed to pop from a small head that seemed to merely exist to support the eyes other a small round mouth like that of a lamprey. Its body was in essentially blue overalls, but it was quite clear this creature was scraggly and supported by essentially a tripod set of legs each ending in wide suction cup like feet.
Looking around the creature gasp at what it saw, the horror the disappointment clear... "What happened? What had they done? Its destroyed, its ruined" it thought to itself unable to speak. Before laid the remains of a ruined city and everything else was a dead waste land. The air in the distance was quite hazy as if filled with ash or soot from a fire.
They had toiled for two hundred years for this to make it only to the surface to see the world from the time of their great ancestors lay in utter ruin. There were no green trees like the myths spoke of compared to the bluish trees that existed underground. Nor green grass, or small animals, no bright blue sky. No that was a hazy orange as if a film filter and been placed between it and the sky changing the color. Red tears poured from its eyes as it felt its hopes its dreams crumble into dust matching the ruined state of the land that it saw before it. "What had the humans done to the world?" it asked itself in painful disbelief.
2 years later:
Over the course of two years the monsters and humans they had befriended often by saving them from the horrors of the wasteland had built up a large fortified settlement. Taking what they could from the underground and the nearby ruined city. King Asgore Dreemurr ruled over the underground and the Hole as the settlement had been named. Apparently after so much time they still hadn't realized that the Goat Lord as some called him in private sucked when it came to naming places.
His wife and queen Toriel Dreemurr rules beside him, having managed to patch things up since the demise of their beloved children. They had decided instead of just making decisions to form a council of various monsters and humans, and one ghoul to decide how things should run in the Hole while everything underground was strictly the province of the two royals.
The Hole proper was roughly a mile radius around the entrance to the underground which was the most fortified spot. The entire settlement was surrounded by a makeshift wall of broken concrete, sheet metal, long dead cars and anything else that was sturdy and durable. It had several makeshift watch towers. A large massive fortified gate that looked more like a medieval castle gate was one of the few ways in and the only way for caravans to get in. All the other entrances which were guarded twenty four seven only allowed two people at most standing side by side to pass through.
Compared to many other settlements that the monsters had encountered in the past two years by far the Hole was more organized and built better. Care and effort went into each building even what would be considered nothing more than one room shacks. Thou granted it still all looked ruined and decayed save for a few buildings that had managed to be painted. Though irradiated rain had left those buildings grungy looking.
Large windmills farther up on what was left of the mountain appeared to provide power to the settlement and while they did it was a ruse. Between the monsters and human scientists they had managed to develop a power generator of sorts that ran off the magma of Hotland in the underground and ran power cables to the surface.
Over the course of the two years the monsters had found out an interesting fact a few actually. First radiation did not affect them. Though they were not entirely sure why. They could become irradiated but if they stayed in a place that wasn't irradiated the radiation would dissipate. They seemed to soak it up and break it down somehow which was strange given energy couldn't just be broken down. Another fact was that the Hole and the surrounding area's were relatively radiation free. But the most useful and important fact was that beings and items taken into the underground were quickly decontaminated of radiation.
Due to those facts The Hole gained fame for having ample amounts of purified food and water as well as being able to cure radiation sickness . Though sadly early on the kind monsters learned they couldn't trust everyone as several attempts from various groups to take over happened. Still they opened their doors to good humans, ghouls, and even a few highly intelligent super mutants at least highly intelligent for super mutants.
Using the fact they could purify things of radiation they built many rain collectors all over the settlement and then sent the rain down to the underground lakes and streams to be purified while bringing up clean water for the citizens as well as some to sell to caravans. About half a mile from the Hole was a large farm and the food grown was likewise taken to the underground to be purified. Magic was used to preserve the food so it wouldn't spoil.
It would seem that in the desolate wastes that had become the surface during the absence of monsters, the underground and by extension the Hole was a paradise and safe haven like no other. Which had earned the Hole no end of enemies who wished to either exploit or keep its unique benefits all to themselves. Mainly raiders were the biggest issue such that as much as they hated the idea the Militia of the Hole actively hunted down raiders within a day's travel of the Hole.
There was a run in with the brotherhood of steel, who initially thought the monsters were some new form of super mutant. But thanks to human intervention the brotherhood didn't try to start a war nor try to force the monsters out. In fact a few of the brother hood mainly older members no longer fit for brotherhood standards of combat retired to the Hole to train the monsters and the humans on the militia.
Super mutants were always a problem typical if more than one showed up as they just couldn't be reasoned with and had a habit of calling monsters freaky freaks that were no good alive and worthless dead since they couldn't eat them for meat.
Finally there was the Human supremacist group called the Guardians that were essentially the remains of what the humans called the Enclave. A group that believe that only humans should rule and be allowed to live and everything else including ghouls despite technically just being extremely irradiated humans should be wiped from existence. Luckily to date the people of the Hole had managed to repel every attack.
There was one dark spot in the Hole's history the... Purists. Lead by a monster named Flowery who absolutely HATED humans, including ghouls unless it was the feral ghouls since they didn't bother monsters, and super mutants who preyed on humans. About a year ago Flowery and his followers tried to stage a coup and take over the Hole which they would have then started exterminating the humans or using them as slaves to work to death, but they were a minority of only about 25 monsters compared to a settlement with a combined population of nearly 200 that lived above ground mostly human. They were banished from not only the Hole but from the underground as the royals had deemed their actions and hatred to be antitheist of how monsters should be and didn't want them to influence the next generation. To date no one knows what happened to them thou they promised vengeance for being betrayed by their own kind in favor of humans.
Thus was the history that was taught in the Hole's school for the history of the Hole, as well as both the history of humans and monsters. How both were needed to survive in this harsh devastated world. Unity and Cooperation were the key principals that everyone lived by in the Hole. One couldn't survive for long in the barren nuclear wasteland.