Whenever I enter my Mind Palace, no matter where I am - be it the subway, a forest, or a hospital ward - white walls come up around me. They are cold and seem to be made of light. This place hasn't always looked like this. Initially I started with a simple apartment which I was furnishing as I saw fit. I used to relocate the furniture and invite guests. In time, the Palace has been changing, morphing into a lofty cathedral with clouds instead of a ceiling; then came a deep dark cave - at that time I was descending into the very depths of my soul to hunt and catch beasts. In the end of it I settled with plain white walls, now that I don't need any decorations or objectification of my inner space. Everything I need is here.
Out of the darkness before me a geometric shape manifests. It looks as if woven from invisible ethereal threads; an intertwinement of glowing rings rotating around a single center point. Rainbow dances on the rings, yet my eyes aren't blinded by the light - they bask in its soft radiance. My Mentor soars up to me and I greet him with a nod.
I've known him to take the shape of a raven, a human, a couple of koi fishes, a double helix. Today his appearance matches his essence almost completely, for what is knowledge if not pure light?
Today is the last time you come to me. I hear his vibrating voice full of rich harmonics. If I was to visualize that sound, I'd have imagined a water surface with fine ripples.
“Why?” I ask as I study the mesmerizing dance of his rings.
After today's meeting you shall no longer need my company. As he speaks, the synesthetic liquid ripples like water resonating in a Tibetan singing bowl. I enjoy watching the vibration of sound waves, the softly quivering sine curves.
The image got you distracted.
I defocus my vision and train my eyes on my Mentor once more whose image was by now getting somewhat blurry.
"Now I've got nothing left but images. Even those start getting insignificant."
That means you're very close now.
"Close to what?"
To realizing the most important thing. Self-perfection has a limit. Every journey has a terminal stage, an apotheosis that negates the very nature of moving forward.
"Why did you never mention this before?"
That would have made an image of a goal appear in your mind. That image is harmful, it distracts one from the process of knowledge.
The walls move apart and space surges towards me and through me, accelerating quickly. I'm dashing through the Universe yet at the same time I remain static, watching as light around me turns to solid bars.
Soon I'm drawn into matter, into its rapidly growing deepness. I zip through the insane empty gaps between atoms - in contrast, the latter look like tiny particles of sand; suddenly, these gaps turn into cosmic voids of unsurpassed scale, and that makes me remember the words of the ancient mystic Trismegistus, ‘As above, so below.' I witness the world looping on itself, shifting to the largest condition from the smallest one, and every Planckian length reveals to me the vastness of outer space. I'm seeing electron shells akin to planetary nebulae and planets akin to tiniest particles. Then my perception readjusts and I see the emptiness that fills 99.9% of the Universe. It is akin to a spreading oil spill and it finds its way everywhere.
Suddenly I feel a shove that throws me back into the return point - a conventional circle drawn on the Palace's floor. I realize that I'm still sitting in its center with white walls rising around me.
What did you see? asks the Mentor.
"Matter and emptiness. There is an immense amount of emptiness, it's the basis of what we consider solid matter. Matter is spread thin and suspended in vacuum. I knew that already."
You think you know much about matter. But you've never gone any deeper than quarks, have you?
"Yes. Whenever I tried doing that, they were becoming pure energy."
Now open your eyes.
I'm not happy about the idea of breaking my trance right now, yet I grudgingly obey. Through the slits of my eyes I see a dimly-lit, sparsely furnished room. There is a table in front of me, with a stack of books and several plates on it. Before it stand several boxes of my belongings which I never bothered to unpack after I moved. A piece of gym equipment near a wall. Grated windows. Soft light is breaking through the matte glass, glancing on the brick walls and shiny floor tiles. My Mentor is still here - weird as it seems, he didn't vanish with the Palace, having shifted to the real world instead. Only the fact that his presence doesn't light up the room confirms he's really no part of it.
Look around. What do you see?
"I see a room. A table. A window. Boxes."
Not quite. You're only seeing their reflection on your retina. Your eyes receive signals from the outside world, and your brain is wired in such a way as to project the processed result outwards. You're dealing with a hologram of your own neural activity.
"I'm not seeing the real world as much as the outward projection of my own neural patterns," I rephrase.
You are a thing in yourself. Everything you see around you only exists in your mind. Light is falling on your retina and your brain encodes it so that you see a locker or a window. Actually, the images that appear in your mind are completely unrelated to those things.
"If there is a light coming from the outside and creating stable images," I object, "that means there are objects that exist independently from me. And I have to take their objective existence into account."
Am I an object? Do I exist independently from you?
"You're not in the room yet I see you. Just as I see the Palace and all the other things that aren't. But there's a great difference between things existing in the physical world and the images generated by my own imagination. The latter are malleable, conventional and subject to my will. The former, whatever they are and however I see them, exist independently from me."
That is correct.
I catch a satisfied breath, realizing that I remembered the boundary between the real world and the world of ideas and images just in time. If I were to visualize it, I would have imagined a soap bubble film, durable but stretching under pressure.
Meanwhile the Mentor stays silent. His cold, concentrated attention focused on me hints that we're not done yet.
"That is quite a mediocre thought. You seem to have something to add."
Exactly. Now listen close. All this time I've been accustoming you to the notion of emptiness. You were meant to become adjusted to it, become comfortable in it. Now you have to make one last step. This step is to forget everything you've learned to this day. It's all not true.
I feel a chill running down my spine. It seems like we're approaching the crucial topic.
Truth is, there is no light falling on your retina.
"I don't understand."
The hallucinations are essentially your brain structures behaving in such a way as if you are really receiving those signals from outside.
"As if these things were really affecting my receptors."
Yes. You will not resolve this paradox unless you understand there are no outside signals. There's no light falling on your retina, no outside world. You are the one who creates it. You are the only one in your head.
"Are you talking about the imaginary world?"
I'm trying to say there is no real world and no imaginary world. There is only one world - and it isn't.
I'm slowly processing what I just heard, trying to correlate it with the designs I've been making my whole life. Slowly, an understanding dawns on me.
For years I have been building a scheme of all creation in my head, a scheme that would incorporate both the objective reality and the crazy things I've been able to see. For years I've been building borderlines millimeter by millimeter, fencing one world off the other, making a place for every thing. I desperately sought a place for myself in that scheme, while studying and developing my own mental capabilities. My Mentor taught me to exist in both worlds; the first one was necessary to maintain my physical body's homeostasis - that is, I had to eat, drink, keep myself warm, supply my neurons with oxygen. The other world was necessary to perfect my consciousness.
Now I have to cast it all away.
"Am I the cause of the world around me?"
By the power of your mind. Your brain is like a hologram projector and everything around you is a manifestation of your perfect mind.
These words pull a certain string in my memory. I concentrate on the vibrating thread, grasp it and obtain the memory I need: a holographic model of the Universe.
"All the information about the creation is written on the surface of my consciousness, and is projected inwards."
Inwards or outwards. Same things, in all but name. Remember your last journey.
I start remembering. I remember how incessantly the words from the Emerald Tablet were coming to my mind: as above, so below. As outside, so inside.
The Mentor's image is no longer before me. His voice resounds in my head, vibrating inside the liquid mental space. I realize the voice I'm hearing is my own.
At this moment every distinction between inside and outside loses any meaning to me. Everything is as he said. I feel elated and gleeful. I fling my eyes open wide, viewing the things around me. I look at the books on the table and see every atom, every tiny clump of divine irony - my irony - they are composed of. I laugh and see that they don't exist.
And they vanish.
I'm looking at the pile of boxes before me. So substantial, so material they pretend to be. Substantiality? I tell them, 'You are not.' And they are not.
"I understand," I whisper quietly.
I unveil everything. I crack open the walls around me - and they are no more. I see the grey, blocky houses, the woods like a greyish green ring around me - and they are no more. I raise my head, look at the sky, hazy with thin misty clouds - and the sky is gone.
I'm frozen in a void, weightless, like a laughing deity sitting in the lotus position, my arms raised. Around me, as far as the eye can see, is only emptiness. I've unveiled every thing, every tiny particle of the outside world, even the air itself. I cast all their shrouds away and reveal there's nothing underneath. Serenity fills me, as deep and final as it can only be in the grave. I turn my attention inside myself. My skull is empty, as if the brain has been taken out, and filled with bluish purple light. Splashes of light dance inside the dome of my cranium, converging into images and unraveling into delicate threads again. I look deeper still and see the same void that I discovered around me. And with relief I realize I am a product of my own mind too.
"I understand." I silently smile before completely cleansing my consciousness and collapsing in on myself.

Excerpt from SCP-2470 recovery log:
"The first report of the object's anomalous activity came on ██.██.20██ at about ██:00 from an airplane observer of FGU “Avialesookhrana”, who was conducting fire safety monitoring in the [REDACTED] area. The pilot reported a huge deforested area centered around a wide, deep cavity. Communication with the pilot ceased soon afterwards. The report was intercepted by undercover Foundation agents in the MES and a reconnaissance operation with █ mobile task forces was arranged. Initial hypotheses regarding the object's nature were defining it as something akin to a miniature black hole. However, primary analysis disproved this point of view and demonstrated the true nature of the anomaly. Several methods of containment and/or neutralization, such as [DATA EXPUNGED] had been applied unsuccessfully, and were followed by a proposal to use “Weißschatten's paradox” in order to neutralize the object. This attempt was a partial success. Neutralization was not achieved; however, it was discovered that the paradox's carrier was not susceptible to the object's effect, which allowed the Foundation to capture SCP-2470 after several unsuccessful attempts and to develop the current containment protocols. Total losses throughout