Heart of Nature

At the depths of our natural world is the very heart of nature itself (also referred to as nature's blasted core, heart of all creation, heart of existence, core of all existence, fundament of nature, core of the universe, etc.), a plane of existence in the world of Dota 2.

Description
Although nature is very much real, what we know is hardly the truth of the cosmos. The reality of reality is that there is a central hinterland deep within the totality of creation, a world that has torment, suffering, and decay as its essentials. This is the heart of nature. Due to its hidden nature, it can be seen thru the haunted Chronoptic Crystals, and those who do so will find a revelation so horrifying and hideous that it alters them irreparably on every level of their being. As such, the heart of nature is lurid and vile. Besides the core of Nature being a world of torment and decay, it is said by Leshrac to be a blasted world, meaning that it's a nature destroyed and damaged. Despite its evilness, it's substantial to the existence of this universe, since it is called the “core of the universe” or the “fundament of nature” to Enigma, the latter name implying that this foul plane is the very foundation of all creation which supports its existence—a starting point for creation from where all things in nature are formed from. According to Leshrac, the physical form generally comes from this plane of existence, which may explain why it is called the heart of nature. If every being's form originates from this blasted plane, then all who have their bodies provided to them from this plane is undergoing an existence of suffering that they have yet to learn until they realize it by seeing this evil truth of nature for themselves, since their corporeal body's origin is a world made of tormented elements.

The Impurities
Akin to the natural world's elements, the Impurities are the elements that form the heart of all creation. As impure elements, the whole that they compose mirrors their properties, thus it's a plane of blight and torment. There are 4 Impurities corresponding with the elements or states of matter: sinister energy, tainted water, evil wind, and brittle earth. Judging by these impure elements of nature, the heart of nature is also hostile, polluted, and broken down to the point of fragility, truly making this plane a realm of utter chaos.

Locations
A malfunction with the reality warping Continuum Device opened the paths to many realms and dimensions in the Continuum Vault, including the Weald of Torment, which is implied to be in the heart of nature. The nihilist Ash the Defiler lives in this forest.

Speculation
Interestingly, the place chosen for Enigma to receive random item drops is the "fundament of nature" or the "core of the universe" where things he calls “treasures” spring from. Perhaps this world was chosen as his source of random drops because it is a chaotic plane, further adding that the heart of nature is also chaotic because of its randomness, besides its impurity and desolation. This also adds the fact that this evil heart of nature does not just create the form itself, but just about anything that Enigma considers a worthy treasure. As such, its power of creation from chaos means that this place isn't just the source of the form, but also the source of creation itself, at least on a material level. Speaking of creation from chaos, this is similar to creation from nothingness. This may bridge the gap between this realm and everything related to it with nothingness since a state of chaos is closer to annihilation or nothingness than a state of order, as the Chaos Knight himself can attest. The core of reality being the source of creation competes in validity with the various creation stories found in Dota 2, such as existence being created from the Elder Titan's great flaw, all of existence being born from the sundering of the Wailing One, the essential threads that compose reality being woven from the Loom, etc.

Notable Inhabitants
Judging by the kinds of people who know or are related with the place, the heart of reality is known to and meant for nihilists only. After all, mere knowledge of this plane is enough to turn anyone into a pessimistic nihilist, such as Leshrac. It is interesting to notice that there seems to be no intelligences native to this plane. The only intelligences here are those that are non-native lifeforms, but rather, visitors like Leshrac (although he, and perhaps all of creation, technically belongs here). Maybe the lack of native sapient beings has something to do with the plane having witless elements, with "witless" possibly meaning that they lack a mind. If there were any native intelligences here, then Leshrac would not have called this place a cloister. But this isn't the case, implying that he's the only creature here.

Heroes
Once a great philosopher, sought the meaning of existence via plumbing the depths of reality with the Chronoptic Crystals. Peering through the haunted Crystals, Leshrac alone saw the horrifying truth of nature at its very core that irreparably warped him into the foul being that he is today, at one with the agonizing unnature that he discovered.
 * Leshrac lives alone in and springs from the heart of nature. When he dies, he is sent back to this cloister to reincarnate.
 * Following this revelation, Leshrac has professed himself as the guardian of this plane's Impurities and an evil agent for nature.
 * Through the Chronoptic Crystals, Leshrac delved into the unexplored depths of creation and learned that the truth of nature is torment, suffering, and decay.
 * As such, he believes that everyone is actually tormented like he is, but he laments that they are utterly unaware of their tormented existence unlike him.
 * Thus, he forces everyone to see the truth like he did by sending them here, returning their form to where it came to return to and become one with the Impurities.
 * Leshrac's discovery of this world and its evil truth are the basis of his evil personality and nihilism, rejecting those who believe the cosmos will reward good.

Characters
Ash the Defiler lives in the Weald of Torment, accessible in the Continuum Vault. The place's name implies that it's in the heart of nature. It's unknown if he coexists with Leshrac.

Flora
Solely based on the plants that grow on Leshrac's body—which is completely at one with this realm and thus it's a reflection of what may grow in there—the heart of nature seems to have its own plant life, just like the natural plane that it supports. Appearing as a growth on Leshrac's body when he drank the tainted waters, there are branches or roots that can channel great but unknown power.

Ridged, climbing vines that are said to be a “twisted sort of wisdom” grow here, feeding and thriving off of their host's anguish, black thoughts, and foul deeds.

Other organisms
Thorny and stone-hard fungi that resemble mushroom caps grow here. They are also said to be unnatural, maybe because they grew beyond their homeworld on Leshrac's body or the world they're from is unnatural. As one of the growths on his form, they may be sustained by the tainted waters that also gave him his other growths, like his arm's branches.

Heroes
When receives a “treasure” of great worth, he will mention its source: a place he calls the “fundament of nature” and the “core of the universe.”  These two names might be referring to a single place and both names are synonymous with the heart of nature, which means that he may be referring to this said plane of existence. This makes him one of the few entities to know about the evil truth of nature. Him knowing this place may also explain why he's nihilistic and pessimistic like Leshrac and Ash. Upon acquiring an, Enigma reuses the second voice line, implying that these runes also come from the core of the universe for some reason.

Trivia

 * The heart of nature's lore may have been inspired by the concept of the world being created from a state of chaos, common in creation myths that depict this world as being made from disorder. Between these stories and myths, chaos may be depicted as a formless heap of mass or pure nothingness, or even a being who identifies as either depictions.