After school one day, the CMC's decided to pay a visit to one of the local Humans who lived in Ponyville, Matt Carson. He worked at the Ponyville Library, and in his free time, he worked as an archivist. An archivist of what you may ask? An archivist of YouTube videos. Contained within his massive collection of videos, every single one of which he downloaded himself, and then burned onto a CD/DVD to create a physical copy, was literally every single YouTube Video that had ever been uploaded to the platform, from Day 1, until the Present Day. Even if a video had been deleted long ago, or had been somehow lost (such as the infamous original "Percy and the Ghost Diesel"), Matt had it in his archive, which was found to be even more extensive than the famed "Wayback Machine" could have even dreamed up.
His entire basement was stacked with massive library shelves and racks to hold his collection, which was divided into various categories/genres, and then subdivided by things like title, length, date, time of upload, and of course, whether or not it was age-restricted. If it was age-restricted, it was placed in its own section away from the other media, and locked up behind a door. In the center of the archive were a series of monitors and TV screens, most of which could be used to watch the media in the archive, while a few were used to search for any video you wanted, just like you would use a computer at a regular library to find the book you wanted.
Like many others in Ponyville, and across Equestria, the CMC's loved to visit Matt, and watch some of the videos in his vast archive. They would howl with laughter at the various fail compilations, "ooh", and "aww" at various animal videos, look on in awe at various documentaries, and even watch transfixed at videos of people unclogging drains, and grooming pets. There truly was something for everyone, and everypony. However, since Matt was often working, and he didn't just want random people and Ponies in his basement all the time, the archive was only open a few days a week, and even then, only for a set number of hours. Luckily, on that day the archives were "open", and after the CMC's entered through the side-door Matt had built into the side of his house, they walked down a flight of stairs, and entered through the double-doors leading into the basement archive.
Once they were inside, the trio looked around them in awe. They never could get over just how massive Matt's basement was, or how many rows upon rows of shelves and racks he had down there, all full of media. Many had asked Matt in the past why he went to the trouble to create physical copies of every single YouTube Video, while also having them available for viewing on the various screens, which had all of the videos stored on a computer database, and Matt told them that it was for redundancy reasons. If anything ever happened to those databases, he would still have physical copies of everything, and nothing would be lost.
"So, what should we watch today?" Sweetie Belle asked as she and her friends made their way over to an available viewing screen, which the trio sat in front of on beanbag chairs.
"Hmm, how 'bout some more of them dog grooming videos?" Applebloom suggested.
"Or what about more of those 'Oshkosh Air Show' videos, as Matt calls them?" Scootaloo added.
Sweetie Belle contemplated looking at more costume-making tutorials, but then she suggested that they just look at the archive, and use the "Surprise Me" feature. Matt added this feature to pick a category of videos at random, and then display them on the screen for the viewer(s) to select. After spinning for a bit, a new category of videos that the Girls had never heard of before popped up.
"Huh. What're 'Lim......Lime.....Lime-all Spaces'?" Applebloom asked.
"I don't know, Applebloom." Scootaloo shrugged.
Sweetie Belle then pressed a red button that Matt had installed near each screen that people and Ponies could push if they ever had questions about something. Sure enough, a few moments later, Matt appeared. He was in his mid 20's, with brown hair, brown eyes, wore glasses, and was dressed in dark pants, black shoes, and a red T-shirt. He also had a tattoo of a black pawprint visible on his left arm.
"Yes, do you Girls need help?" He asked kindly.
Sweetie Belle spoke up. "Yeah, we were wondering what this category of videos was, as we've never heard of it before."
Matt looked at the screen, before smiling. "Ah, it seems you've girls have found the 'Liminal Spaces' Category."
"That's what we were confused about. What're 'Liminal Spaces'? Is it something scary?"
Matt half shook his head, and then nodded, before shaking his head again. "Well......yes and no. Some think that they're scary, but others enjoy them. Some see happiness in them while others feel nostalgia, and some feel unease." Noting the looks of confusion of the Girls's faces, he explained further.
"By the textbook definition, Liminal Spaces are described as 'The subject of an internet aesthetic portraying empty or abandoned places that appear eerie, forlorn, and often surreal. Liminal spaces are commonly places of transition, or nostalgic appeal, pertaining to the concept of liminality.' This is what makes Liminal Spaces so unique. No two are the same, and a picture of different ones can elicit so many different feelings, including what I mentioned above. In many cases, Liminal Spaces can feel very familiar to people, as they may look similar to places that people have been before, or seeing a picture of a Liminal Space can unlock a memory from your past, such as your childhood." Matt then began to show the trio a few examples of Liminal Spaces.
"Hey, I've seen that last image before!" Scootaloo piped up. "That's the Food Avenue Express Restaurant that that Human named Scar Fox opened up here in Ponyville a few years ago."
"You're close, Scootaloo. Yes, this is A Food Avenue Express Restaurant, but this one is, or rather, was, located back on Earth. But it's still a Liminal Space."
"Why're these spaces so empty?" Applebloom asked. "There ain't nopony in any of 'em."
"That's the point, Applebloom. Part of the aesthetic of Liminal Spaces is their total lack of people or animals. They're transitional spaces, leading from one place to another, which is why you see a lot of these pictures being taken in dark, empty, closed, or abandoned places. And how do you Girls feel after looking at these pictures?"
The CMC's thought for a moment.
"Well, I felt like I was looking at places that were simply closed for the night, and awaiting reopening in the morning." Sweetie Belle replied.
"They....kinda felt familiar to me, even though I haven't seen them before." Scootaloo said slowly.
"They felt....kinda eerie to me. Like somethin' was watchin' from the shadows, especially that house n' gas station pictures. Maybe it didn't mean no harm, but it still felt....off." Applebloom finished.
"And there you have it. Everyone views Liminal Spaces differently, and everyone feels something different when you look at them. However, remember what I said earlier about how Liminal Spaces could unlock feelings of nostalgia?"
The Girls nodded.
"Well, here's some examples of that." 
"I cannot understand it. Why does EVERY SINGLE arcade, skating rink, play-zone, movie theater, etc have THAT carpet??" Scootaloo asked.
Matt laughed. "Nobody knows, Scootaloo. I've asked myself that same question so many times, and no one seems to have an answer for it."
After talking to the Girls about Liminal Spaces for a little while longer, he left them to watch some more videos about the topic, and they were soon immersed in watching various compilations of Liminal Spaces, from normal, to nostalgic, to creepy.
After watching for a while, the CMC's tried to watch a video called "Liminal Spaces but with Calm Nostalgic Music", but for some reason, the video wouldn't play.
"Huh? What's wrong with it?"
"I dunno, Applebloom." Scootaloo said as she clicked the mouse a few more times. "It just says 'Error, Unable to Play'."
"Is it age-restricted?" Sweetie Belle asked.
"I don't think so. If it was, then that gray screen saying 'Age-Restricted Content. Please ask for Assistance' would've popped up as soon as we clicked on it."
"Hmm, well, could we see if we could find the physical copy of it on the shelves?"
"Yeah, we could do that, Applebloom."
Scootaloo then walked over to one of the archive computers, and once the Archive Search screen popped up, she typed in "Liminal Spaces but with Calm Nostalgic Music", and pressed "Enter". After a few seconds, the computer beeped, and the result popped up on screen.
"Ok, the physical copy's in the Archive's 'Art' Section, Subsection 'Liminal Spaces', Subsection 'Surreal', under....."
"Just get to the point already, Scoots!" Sweetie Belle interrupted. "Where's the video at?"
Scootaloo rolled her eyes. "Yeah, whatever. Follow me, Girls." She then led the way to where the video's physical copy was located. When the Girls arrived, Scootaloo climbed up onto one of the Archive's many rolling ladders to get the CD case the video was in, and made an unusual discovery.
"This is weird."
"What is it, Scoots?" Applebloom asked.
"It's locked up behind a glass case."
"Huh? What does that mean?"
"Just what I said, Sweetie. I mean that the video we want is at the end of the shelf, right where it should be, but I can't grab it, because it's locked away behind a glass case on the shelf just large enough to hold it. The rest of the shelf looks normal, save for that glass case, or whatever it is. And there's a yellow sticker saying 'Cognitive Hazard' on the front of the case, whatever that means."
Scootaloo then climbed back down, and the 3 of them looked at each other, unsure of what to think. They then decided to go find Matt, and ask him about it. Since they were close to the desk where he often did his work while down in the Archives, they walked over to it.
"Hey, Matt?" Scootaloo asked.
"Hmm?" Matt looked up from the slices of pizza he was eating. "You Girls need help with something?"
"Yeah, we were trying to watch a video, but for some reason, we couldn't watch it on the main screen; all we got was an error message. And no, it wasn't age restricted."
Sweetie Belle then took up the story. "We assumed it was some kind of error, so we went to look for the physical copy of the video in the Archives, but it was locked away behind a glass case on the shelf, and there was a sticker saying 'Cognitive Hazard' on the front of the case."
When Matt heard their story, his smile faded, and he seemed to be almost sad. "Let me guess. You Girls tried to watch ‘Liminal Spaces but with Calm Nostalgic Music’?"
"Yeah, how'd ya know?" Applebloom asked.
"Because out of my entire Archive, save for the Age-Restricted videos, that's the only one I withheld from the public, both on the screens, and the physical copy."
"Why though?" Sweetie Belle asked. "Is it something bad?"
Matt shook his head. "No, it's not bad. In fact, it's little different than most of the other Liminal Space videos, for the most part at least, but for me....this one just hit different. It..." He paused. "....It was just too real for me."
"What do you mean by that?" Scootaloo asked.
Matt didn't answer right away. He looked like he wanted to say something, but was trying to find the right words first. The CMC's waited patiently for him to finally speak.
"Does.......it have some special meanin' to ya?" Applebloom finally asked.
Matt nodded slowly. "Yes....it does. Out of all the pictures in that video, so many of them were familiar to me. They looked like places I'd either been to, or seen before; places from my childhood. Seeing them unlocked memories inside of me that I didn't even know I had; memories that I had forgotten about long ago. Memories of a time that was no more, from places that were no longer there, in some cases. Times change, places get remodeled, locations close, people move away, and most of all, people grow up. That's one thing that you can never escape from, growing up."
He then looked down at the CMC's, a deep sadness on his face. "What I'm about to tell you Girls is probably going to be one of, if not the most important life-lesson you'll ever receive, so please heed it well."
The Girls nodded, wondering what kind of wisdom Matt was about to impart upon them.
"How old are you Girls? 9? 10?"
"I'm 11, and Scootaloo and Applebloom are 12." Sweetie Belle replied.
"So it's almost too late." Matt murmured quietly. "I should have told you Girls this a few years ago at least, if not later."
"Tell us what?" Scootaloo asked, wondering where Matt was going with what he was saying.
"One of the harshest, yet saddest truths about the reality of growing up. You Girls want to be all grown up, right? To go out there, and do all the things your Big Sisters get to do?"
The CMC's agreed.
"Well, your goals are no different than those of many other kids your age, Human and Pony alike. Heck, when I was a kid, all I wanted to do was grow up so that I could do more stuff, and it wasn't until far too late that I realized my mistake, and when I did, all I could do was despair, because there was no changing it now. I was an adult by then." Matt looked at the CMC's. "You Girls need to cherish your childhood; enjoy it to the fullest while it lasts."
"What do you mean?" Scootaloo asked.
"Just what I said, cherish your childhood. You'll have your entire adult lives to enjoy being an adult, but being a kid? You only get to enjoy that once in your life, for a handful of fleeting years, and once that's over, it's over for good. One day, each and every one of you Girls will wake up, and realize that you're not a kid anymore, and you never will be again. Your childhood is over forever, and now all you'll ever be able to do is look back at the memories of the times you had. Don't make the same mistake that me, and so many others have done. We spent almost our entire childhoods trying to grow up, completely oblivious to how we were living the best years of our lives already. And by the time we came to begin to appreciate them, it was too late. We were already teenagers, and soon after that came adulthood. Only then did I look back, and realize what I had lost. I had lost my childhood because I was too blinded by wanting to be an adult. Cherish your childhoods, Girls. Cherish them, and hold onto them for as long as you possibly can, and enjoy being a kid to the fullest extent, because if you do it right, when you do finally become an adult, you'll be able to look back at your childhoods with nothing but fondness, instead of sadness and regret like I do. Sure, I have plenty of happy memories of being a kid, but it's also surrounded by the sadness that I didn't live it to the fullest because I was trying to grow up too fast."
When Matt finally finished, the CMC's looked at him in utter shock. None of them had even the faintest idea of what to say, yet deep down, they knew that what he had told them was the truth. And they themselves were guilty of the very thing Matt had warned them about; trying to grow up too fast, and not cherishing their childhoods while they lasted.
"I know, it's a lot to take in all at once." Matt told them quietly. "It has been for the many other kids I've told this to in the past, and will be for many more to come. It wasn't too late for them to cherish their childhoods, and it's the same for you Girls now. I have a good feeling that one day, you'll come back and thank me for what I told you here today."
For a while longer, the CMC's talked in-depth with Matt about cherishing their childhoods, and living them to their fullest while they lasted. It was quite the eye-opening experience for all 3 of them, and for Matt too, as he told the CMC's about his own childhood, and the memories he had of it, and this gave the Girls an idea.
"Matt?" Applebloom asked.
"Yeah, Applebloom?"
"What if......what if ya watched 'Liminal Spaces but with Calm Nostalgic Music', but this time, we watched it with ya? Helped ya get through it, and come to terms with it?"
"Yeah." Sweetie Belle added. "You did so much in helping us understand the value of cherishing our childhoods, in return, we want to help you get through watching that video again."
"And perhaps finally overcome my regret of not cherishing my childhood to the fullest until it was far too late." Matt finished. "That's.......well, under most circumstances, I'd just brush it off, but coming from you 3........I don't see the harm in at least trying."
Matt then moved over to the computer next to him, and after typing for a moment, he imputed an Admin code, and unlocked the video in question, allowing it to be viewable by everyone and everypony again. He also wrote on a Post-It Note to remind himself later to unlock the glass case containing the hard copy of the same video. Once he was done, he grabbed the rest of his pizza, and joined the CMC's at their viewing screen, and after Scootaloo clicked on the video, and it loaded up, the 4 of them watched it together.
It had been hard for Matt at first, but with the CMC's with him, and pausing the video at times to talk about certain things, he was able to get through the entire video, and then he watched it a few more times until he was able to get through it without pausing, and felt little more than nostalgia. Once they re-watched the video one final time, Matt looked at the trio.
"Thank you. What you Girls have done for me today is........hard to put into words, but it feels like a great burden has been lifted off of my shoulders, and I can finally move on with my life, without constantly being reminded about my failure to have cherished my childhood. But my message to cherish your childhood remains unchanged."
"You're welcome, Matt." Scootaloo told him. "I'm glad that we were able to help you overcome this."
"Yeah", Sweetie Belle agreed. "And thank you for helping us realize how important it is for us to cherish our childhoods while they last."
Applebloom agreed, and they all talked about this for a while longer before the Girls went home for the day, and Matt got back to work for the day. He knew that he'd made an impact on the CMC's with his life lesson, though he knew that he still had a few years yet before he would see the result of his work.
About 10 years later, Matt was still maintaining his video archive in his basement in Ponyville, and people and Ponies were still stopping by, though now many of them were grown up, some even now bringing their own kids with them. Matt was busy at his desk, hard at work creating some physical copies of the latest round of YouTube videos, while also planning on building more shelves for these, and other physical copies, when he saw several Ponies step up to his desk, just out of his field of view. He looked up at the 3 Ponies who stood in front of him, confused for a moment, but then his eyes widened in shock. It was the CMC's, but now all of them were grown up
"Gosh, is that really you, Girls? If so, then you've really grown up!"
The 3 of them laughed a bit. They were now 21 years old, graduated high school, and while Applebloom still worked at Sweet Apple Acres, Sweetie Belle had been going to school to learn how to be a fashionista like her sister Rarity, while Scootaloo was working at a skateboard and scooter store in town.
"This day's been a long time in coming, Matt, but it happened, just like you said it would." Scootaloo began. "One day I woke up, and realized, 'Gosh. I'm 18, I just graduated high school, and I'm not a filly anymore. My childhood is now over."
The other two agreed with her, and then Sweetie Belle spoke up. "And while it was a shock, and there was some pain to it, it wasn't nearly as bad as we were expecting."
"Oh? And why's that?" Matt asked, already having a feeling about what they were going to say.
"Because of what ya taught us here in this very basement archive almost 10 years ago now. We'd cherished our childhoods, enjoyin' each and every moment of 'em, and now that they're over, we can look back with some sadness that it's all over, but with plenty o' fond memories!"
Matt smiled. "That's great to hear, Girls. It always makes me feel good when I learn that people and Ponies take my words to heart, and cherish their childhoods, and in your case, it all happened because you 3 were curious about Liminal Spaces."
"Yeah, and we're very thankful to you for what you did for us, Matt. And we've been telling our friends, and others we've met over the years about what you told us, to always cherish our childhoods, and enjoy being a kid while it lasts, and many of them also took your words to heart."
"That's great to hear, Scootaloo. I'm so happy to have had such an impact on your lives, and the lives of others."
They chatted for a little bit longer, but eventually the Girls left, as they had to either get back to work for Applebloom and Scootaloo, or get back to school for Sweetie Belle, and Matt smiled again as he watched them go.
"Those 3 never cease to amaze me, even after all these years." He thought to himself. "I'm glad that I was able to help them along on the great journey called Life." Matt then turned back to what he was doing, as those physical video copies weren't going to make themselves.
THE END