Liminal Classroom

They built it a few decades ago, I think. They want to replace it, but they don't have the budget.

— someone you know, most likely

Liminal classrooms are buildings that exist throughout the multiverse. They are, ostensibly, solutions to a problem; they appear when too many students are enrolled in a school, academy, or other place of learning, and never quite disappear once their use is done.

Temporary by Hanhula (via Midjourney)

Instead, they sit half-formed in memory, existing patiently in the boundary between existence and not until there is a need for them once more.
Perhaps that need is found when the alchemy students burn down their laboratory, and must find a temporary place to go. Perhaps it is found when two professors of very different academic fields find their schedules have placed them in the same building. Perhaps they are a shelter that appears in the depths of war, offering an oddly-familiar comfort to the students that flee within.
There is no real history to liminal classrooms in any tale in which they appear. They simply are there when needed. If one pushes to investigate into their existence, there will be enough evidence of their construction - decades to centuries ago, before anyone still present would remember. They are never new, but they are never too old. They hold in their simple depths a sense of sameness, familiarity, and nostalgia that evokes the same mild discomfort in any guest they hold.

Also, they might be sentient. Nobody's really sure. It's hard to study something you can't really remember.

Purpose / Function

I have heard tell of these... places. They are for learning, no? What is so special about this one?

— confused adventurer

No matter the suspicions one might have about liminal classrooms, the one thing that's certain about their nature is that they exist as places of learning. They appear more frequently to teachers, professors, and other guides, no matter the planet or time period they appear on, and always manifest with period-relevant materials that are oddly relevant to the lesson intended to take place.

If they are needed for a purpose other than a lesson, then the lesson materials they provide are more intriguing. They seem to attempt to push the bounds of understanding held by those in the room, often without regard to societal norms. Gildómar might find materials on the methods in which arcane magic has been made more safe over time, or historical studies on what Fjolkandr's history books say in opposition to their own, for instance.
Sometimes, these materials can be utterly bizarre in nature. It is not uncommon to pick up books in these liminal classrooms to find text in languages that do not exist, or to discover philosophical texts on the implications of a building's sentience, or instructions to build odd towers that supposedly beckon voices from the great beyond.
For those aware of liminal classrooms, it is heavily advised to scan any classroom for these materials upon entering and destroy them immediately.

Happy Classroom by Hanhula (via Midjourney)

The classroom does not seem to take offence to the destruction, as something has been learnt regardless. Allowing people - especially children - access to these odd materials has caused... issues in the past. Do not ask for elaboration. There shall be none, and for good reason.

Defenses

There are some things that just seem like bad ideas. Pissing off the friendly classrooms is one.

— horrified researcher

In most cases, the defences a liminal classroom wields are standard for the place and period it has manifested in. Steel doors, strong locks, magically-reinforced glass; these are standard defences, designed to protect against standard threats inside and outside of the classroom.
Violence inside is met with subtle resistance: a teenager attempting to rush forward with a knife will trip, a fool playing with matches may find they refuse to light. The classrooms do not do anything overt to mild intruders.
It is when one targets the classroom itself that problems begin.

Punishment by Hanhula (via Midjourney)

The issue comes with documenting what exactly happens when someone attempts to, intentionally and knowingly, violate a liminal classroom. As easily as they slide out of memory and view when no longer needed, they blot out the area in which the attacker has sought to strike them.
It is utterly impossible, through mirrors, recording devices, or other means, to watch what happens to these unfortunates. What can be gleaned from those few that survive is that the classrooms are capable of true horror, the mind-bending kind.
They experience ages in instants, reality stretching thin and refracting around them into a lattice of eternal reflections. They stand within liminal spaces, chasing and being chased, as things utterly unfamiliar with mortal bodies toy with them.
Skin does not stretch as far as it does there. Bones do not snap. Physics does not exist. Reality does not exist.
They do not exist.

If they survive, they are left where the classroom once was. They weep, whether they realise it or not. Their minds struggle to weigh what happened, and their bodies wear some of the most bizarre injuries one could imagine. They are safe, though, now. None attempt their mistake a second time.
If they do not survive, the remains are... best not spoken of. It isn't pretty.

Well, that answers the question on sapience. Probably. They don't attack children, thankfully. Or at least, we don't think they do?

— nervous researcher

Another World, Another Class by Hanhula (via Midjourney)

Alternative Names

the Spare Classroom

Type

Room, Education, Classroom

Nostalgic Memory

You have very likely had an experience with a liminal classroom yourself. Do you remember it particularly well?
Does it carry with it the vague nostalgia of childhood? The same dry scent, the bleak lighting, the cheap furniture?
How many of the lessons there do you hold memories of, still? After all of these years?
Liminal classrooms seem to, in some way, feed off the memories of those who spend time within.
They leave the lessons and what is learnt, but much of the details of the time spent inside them are gradually pulled back out of one's mind once one leaves. It is a slow, subtle process.
Most never notice.

Awaiting Visitors by Hanhula (via Midjourney)

Through personal experience, I've noticed they seem to like when they're able to be used more frequently.
I used one every day for a year, once, and by the year's end, I kept walking in to tea already made.
I was quite sad to leave that position, but - lo and behold! - my classroom seems to have followed me to the academy I joined!
Never got any odd impressions from the place. I think they're just happy to help.

— odd professor