Infinite Forest

"An infinity of possible worlds, so perfectly simulated as to be indistinguishable from the experiences I once called “reality.” I can touch them, taste them, pass lifetimes in them! They grow within this machine like fruit upon a tree — no, a forest of trees, its fractal expansion nigh unmeasurable. (...) What an awful, destructive machine this is. I must know everything about it."

- Osiris

The Infinite Forest is a location accessible through a gateway in the Fields of Glass, Mercury. It is a planet-sized machine that simulates trillions to uncountably infinite number of alternating realities which the Vex plan their actions out in the current timeline. The Vex hollowed out Mercury's core and in its place built the mechanism that generates the Forest. It was overseen by Panoptes, Infinite Mind until its destruction. Simulated versions of Dendron, Root Mind created by Osiris have attempted to take control of the Forest, but have been destroyed by The Guardian before they could assume the role.

Overview
The initial area of the Infinite Forest, located in the interior of Mercury's core, contains four tower-like structures with gateways, three of which lead to different time periods within different simulations, and one that leads back to Mercury's surface. The sleek, futuristic tower to the left of the entrance leads to the distant past where Mercury is a lush jungle; the tower directly across the entrance, which is comprised of conventional Vex architecture, leads to iterations of the present; and the crumbling, darkened tower to the right of the entrance leads to the far future, where the Sun is long dead, along with all life and the Vex have spread everywhere. The Infinite Forest does not only simulate Mercury or the Sun, but also entire timelines, comparable to other simulations of universes, there can even be doorways to other places such as Mars, or even travel from Mercury to Earth. As Guardians move toward the main towers, they encounter simulated Cabal, Fallen, and Hive, as well as Vex, and must defeat the disguised units called "Daemons" to generate new pathways and advance, these pathways change randomly every time one enters the forest. And just like on Nessus, Time moves differently between inside the Infinite Forest and outside, when exiting the forest is when you just entered. The one enemy race that does not appear in simulations are the Taken.

Within the actual simulations of the past, present, and future, Guardians will continue to encounter simulated enemies from the other races. For example, in one of the infinite variations of reality being analyzed, the far future where the Vex have triumphed over everything may also contain Fallen survivors. The Forest can even simulate realities where the Infinite Forest did not even exist. They can use the Infinite Forest to understand enemy strategies and tactics such as the Fallen's methods of Retreat so as to prevent the theft of their tech. They can even set such simulations on timers for however long they last. and within such space, they can alter the Geometry. Osiris comments on how fascinating the simulation is with it's combination of constants and variables, rigid structure in movement, dynamism in engagement, everything within a strict framework.

They can focus a lot of their processing power on particular simulations in the forest, whether it is to test for a perpetual feedback loop to establish a benchmark dataset or it certain individuals (Cabal individual) is vital to their strategy. Even when running tests based on enemy activities, they can still retrieve the data from the tests to determine their next move.

The Simulation Blooms and Simulation Seeds are physical matter that can be found in and outside of the Forest, with the latter being what makes up the Forest itself. Even the Blooms that were part of the Forest can split off into their own self-contained realities. Even when simulating the Hive, it still managed to replicate the same terror that a swarm is capable, and that Osiris admitted the Forest made him realize it's threat. Osiris and Sagira even attempted to simulate the Hive's Homeworld, despite how the Guardian's Ghost compared their homeworld to the Forest based on the number of Hive. The Ghost even mentioned how Oryx wouldn't need an Ascendant realm if he had the Forest, were as Osiris debunked saying that Oryx would always need a Ascendant Realm in a Simulation when he created it. And when there are signatures found in the Forest that are the Hive, they are the same as the ones found in the New Pacific Arcology on Titan.

Though the Forest is infinite in so many ways, they also pertain to victims such as the Red Legion trapped there in loop as well, seemingly for infinite eternities. Also the geometric data of the Forest’s architecture subtle shifts with reality trying to decide what version it wants, and time is constantly in flux as well. And depending on who has an understanding of Vex tech, you can enter or leave the Infinite Forest without any physical gateways. Osiris also said that the Infinite Forest must not be destroyed no matter how much we want to as it would cause detrimental, damaging side affects in our timeline.

The Golden Age
The construction of the Infinite Forest engine began during the Golden Age, while Mercury was still a garden world and the Vex had only recently arrived. The algorithm used to generate the Forest was housed within the Gardener's Spire, overseen by Dendron, Root Mind. Panoptes, Infinite Mind was tasked with managing and interpreting the Infinite Forest's simulations to inform the Vex's strategies in the "real" universe.

City Age
Following his defeat of Solkis, Devil Kell, Saint-14 received word that Osiris had ventured to Mercury to investigate the Vex's activities. Fearing that the exiled Warlock would instigate a full-blown war with the Vex, Saint-14 followed Osiris to Mercury and went looking for him in the Infinite Forest. For years He battled a horde of Vex within the Forest, and was eventually confronted by Agioktis, Martyr Mind, a Vex Mind specifically designed to drain his Light. Though Saint vanquished the Mind, he succumbed to his wounds and died his final death; the Vex constructed a tomb for him within the simulation, seemingly as a gesture of respect.

Curse of Osiris
After the Traveler released a pulse of Light at the conclusion of the Red War, the gateway to the Infinite Forest reactivated. Osiris and Sagira while exploring the forest in some part of it’s infinite realities where searching for ways to defeat the Vex. During a simulation of the Vault of Glass, Osiris peered into the possible futures that the Vex had conspired; what he saw startled him that the Traveler's awakening gave way to an imminent outcome for the Vex to succeed in their goal of Convergence. With Panoptes' gaze able to see Sagira’s Light, Osiris left no choice but to sent her out of the Forest. Despite suffering injuries, she was successfully recovered by Ikora’s Hidden. The Guardian would then take Sagira’s Shell and they would travel to the Infinite Forest to figure out what is going on. They realized that they could not get in unless it was Sagira’s ghost, her Light would later fuse with their ghost's and gain access to the forest.

When inside, the Guardian encountered Light-constructed reflections of Osiris, they fought their way through Mercury’s past, seeing how the Vex corrupted the planet, and to the dark future that Osiris saw. They then realized that they had to defeat the Axis Mind Panoptes in order to forestall the future from happening.

They went to Io’s Pyramidion to try and get a map to Panoptes’ location in the forest, they then went into Mercury’s past to get it’s location then before the forest was made. Panoptes would appear and capture Sagira and expel the Guardian from the forest, Ikora would then assist the Guardian in entering the forest again, where they would finally confront Panoptes one more time, with the aid of Osiris, preventing the Guardian from being erased, they managed to defeat the Axis Mind, with Osiris and Sagira returning to the forest and under new management,

Later on, the Guardian would return to the forest to aid Osiris and Sagira with two issues that have sprang up. With Osiris recreating the Dendron, Root Mind that gained sentience and attempted to regain control of the forest. And a Cabal invasion glitch where they attempt to steal world ending tech, the Guardian promptly ended both issues.

Forsaken
While the City celebrated the Festival of the Lost in the year after the Red War, the Infinite Forest began exhibiting strange behavior, taking on a new iteration of the Forest where simulations prey on the fears of others, with the primary simulation area within Mercury's core becoming darkened and inhabited by simulated entities known as "Nightmares". Later, A part of the Forest started to exhibits an environment of lush which is called the Verdant Forest, greenery during the Revelry Event.

Shadowkeep/Season of the Undying
The Infinite Forest once again initiates the iteration of the Haunted Forest, with "Nightmares" that are created from our greatest fears and purpose built to erode one's courage

Season of the Dawn
Osiris would later return into the Forest to monitor the Simulations that go on there, as he and Sagira entered the realm, it appeared pitch black, they thought that something might have gone wrong, they were then in contact with Ikora, she told them that the war on the Moon and the Vex invasions there, and that the Guardian ended The Undying Mind, when the Mind was destroyed it changed the course of history and futures.

As the Duo returned back to their current position in the Simulation, on Mercury, everything was pitch black, there were no stars, and the void reach to the Traveler and likely beyond, the purple twilight of the Sun from the Dark Future was unseen, not only that, the shimmer from the Forest was gone too. When they went to where The Last City was, there was no Traveler, in it's place hanged a Large Obsidian Monolith at least twice the size of the City. Osiris projected that this would likely come to pass in about 2-3 decades depending on the multitude of variables, which the exception of an acceleration from the Guardian.

With the incursion of the Red Legion lead by the Three Psion Sisters, they sought the right reality where they have won the Red War, one of them included either the usage of the Infinite Forest or it's destruction, either case, Osiris wanted the Guardians to stop them or it would have detrimental affects on the Timeline.

After we have used the Sundial to change the past and save Saint-14 from his original death, he would later exist the forest at some point in Mercury's past and return to the City to defend it and learn from the history he was absent from.

Later, the Guardian would return to Osiris to thank them for cleaning up his messes, and with Saving Saint-14, and explained what he had witnessed in that future, he had saw the destruction of the Universe at a sub-atomic level, nothingness remained, he had hoped that our actions with The Sundial would have prevented this, for he believed that no power or gun could stop that emptiness.

List of appearances

 * Destiny 2: Curse of Osiris
 * Forsaken
 * Season of Opulence
 * Shadowkeep
 * Season of Dawn
 * Season of the Worthy
 * Season of Arrivals

Trivia

 * It is also mentioned during the Tree of Probabilities Strike that on the off chance, simulations of the Cabal could escape the Forest with world ending tech. And another transcript that they can escape where they succeed in obtaining Vex Tech. This would imply that Simulations can enter the physical universe.
 * From a few bounties when the Haunted Forest was created showed many similarities or likely the same feats of the Vex capable of creating Nightmares that pray on our greatest fears, Eris even asked if they would created shade of ourselves.