I think I figured out what the in-world "Summoner's Rift" actually is.

So it was confirmed once by a Red that the Rift is an actual location in the world of Runeterra, even with the IoW not existing. So someone once build this gigantic structure right in the middle of nowhere. But for what reason?

Given that no other party in lore seems to even know it exists, that means it must be in quite some remote/politically-economically irrelvant or maybe even dangerous region. Which means that either the entire civilication that build the rift vanished around it, eradicated somewhen in the Rune Wars, or that it was hidden there on purpose.

But what purpose could the Rift have? Just why would you have a gigantic mountaintop turned into a battlefields where beings from all over Runeterra appear to punch each other's crystal to death, only to repeat the process over and over and over and over again with some variation in the summoned beings?

And what benefit could the builders of such a place draw from it? At first glance, pretty much nothing, unless they want it to be an infinite generator of salt, which is also valuable in medival societies, but probably nowhere near the point that it would justify the effort of building the darn thing.

But there is actually something you can get from this: Information. Being able to summon all sorts of beings (if they are real, parralel existences, or mirror images that just exist in this little world has to be debated at a later point) allows to run COMBAT SIMULATIONS. For once for training, for the other to allow predictions about the future: Runeterra is a world drowing in war by our modern day perspective. Even in our Middle Ages, war has been a completly normal tool in the arsenal of interstate relations. "Peace" did not mean the same as it does today. Like, when I say today that Germany and France are at peace, I mean that the very idea that these countires could attack each other is downright nonsencial, and everyone who thinks otherwise is probably a serious nut-job. In 1913 Germany and France were also "at peace", but that peace was literally just "an temporary absence of war", that could easily change from one day to another.

And that second scenario is what is normality for Runeterra, even more so in the past with the Rune Wars.

And now, imagine the chaotic Sengoku-era in Japan: countless factions tearing each other apart in a civil war. And NOW imagine that more than half of these faction have a weapon of nuclear-bomb-class at their disposal, in this case, a world rune - and that they are not hesitant to use it.

This is the reality of Runewar-Runeterra.

And to operate within such an extremly dangerous enviorment as a nation or tribe, you need information. Who can you trust? Who will betray you? If group A and group B fight, who will come out as a winner? What if the battle is intervened by a thrid party? What is the extent of their individual power? Can you start a fight with a group or is it smarter to abide to their demands instead of risking obliberation? Who are the best allies?

Information is Power, and being able to run hundreds, of not thousands of such simulations, allows stochastic calculations that might even come close to "predicting the future" - and even with with some margin of error that is an extremly powerful tool, which would also explain why the location is quite "hidden" as it seems. After all you wouldn't want to let this fall into the wrong hands.

But how does it work? Well, for that I am grateful for a Rioter to once confirm the existence of "leylines", a network of magical power-lines that occur naturally, forming a network over and through the planent. From a world-building perspective, the existence of such lines changes things quite a lot. My theory is that the rift is directly build on a massive intersection of such ley-lines, where as many of them as possible cross.

From there on, the Summoner's Rift accesses a natural magical network that encompasses the entire globe, and draws information from it.

The theory goes as follows: Individual "A" has impact on the world. Impact on the world means also impact on the leylines. The moment a minimum degree of "impact" -set by the creators - is met, information gets collected and formed into a perfect copy of "Individual A" to appear in the Summoner's Rift. Repeat the same for Individual B and observe their interaction as many times as needed. As allies, as foes, etc. etc. Not-as-impactful individuals supporting them would be simulated as minions.

However, this would also explain where the biggest flaw of such a device lies: flawed input values. The civilication that build the rift is no longer around, which means they got defeated. But how can you be defeated when you have such predictive power? Simply by having the "impact" value set too high for when the Rift considers an indiviual on the world an "relevant champion". One or maybe even several key-indivuals kinda "flew under the radar" and ruined their calculations, effectively leading to their downfall. Another possibility would be that the Rift cannot access "all" of the leyline network and that there are "blind spots" of some sorts.

And today? The builders are gone, but the Rift is still running, infinitely powered due to the leyline-nexus it is sitting on. And so it does what it was made to do: running simulations for all kinds of scenarios while drawing information from the global leyline network.

But from an outsider's view this would probably look different: a mountaintop where regulary explosions can be heard, and dangerous magical discharges happen in completly unpredictable intervals. People who have tried to climb the mountain have been frozen by giant Ice Arrows, blasted into pieces by hextech bombs, had dark spheres knock them into their deaths, had energy blasts slicing their heads of, had their bodies cut apart by wind alone, were frozen by true ice that was suddenly creeping from the top, and so on and so on.

Pretty much everything that would "fall of the map" would be lethal to a normal climber or even someone remotely close to said mountain, so it wouldn't be weird for the entire area to be deserted, because "of the strange phenomemon that has been raging since the Runewars", which the world itself has really no shortage of. And given that the Rift might be running dozends of simulations at once, it wouldn't be weird for the mountain to be constantly shrouded in a maelstrom of magical energy blasting out, truly giving it the impression of a fucked up weather phenomenon, even if it is not visible from "inside the simulation".

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Tl, dr: SR is a gigantic artifact for simulation purposes, drawing information from a global network of power-lines. If there is a connection between the "summoned being" and "original individual" beyond one being a copy of another is unknown.

Furthermore, the artifact itself is extremly dangerous should the world learn of it: the position of a leyline nexus this powerful alone would be enough to start a world-war in struggle for control of it, the technology being just the icing on the cake. Imagine not only drawing information from the leylines, but also altering them. One would be able to alter the magical structure of the planet, power that goes far beyond a simple world rune. I doubt many could resist such godlike-powers, and a lot of them would set the world ablaze to get their hands on it.