The "Borderworld"
All about the world of Xen itself and what it is

The "Void" - The Space Beyond All
The Void is a concept unique to the Vortigaunts, never really spoken aloud and rarely discussed. A realm of mystery.
It is often misunderstood as its own dimension or its own world- and in a sense it technically could be such, but not to the same degree as Xen, the Borderworld nor the planet of Earth. It is instead a section of multi-versal silence that exists at the fringes of perception and reality, a place between Dimensions that encompasses creation as a black empty blanket of nothingness- a shadow described by the Vortal Tribes as the Absence of Being, others as a "forgotten shadow cast by the Universe itself."
A few witnesses are aware that a few Vortigaunts call out as one of their chants and battlecries towards their foes with the saying "To the Void with you!". It does not mean that they are to literally banish their enemies, but more or less as symbolic condemnation: to be cast into that which has no memory, no identity and no rhythm in the Continuum. A solemn erasure from the song of the Universe.
The Void is not a subject present within any standards of education, nor is its presence recognized. But amongst Vortal Tribes, it is always and forever felt amongst the Vortessence- a looming awareness in minds stuck in deep mediation. To Younger ones, it is merely taught as superstition- one of restraint and a lesson on humility while the older and more atuned members, it is a boundary that shall never be crossed- an echo from before time was bound to form. The Grand Elders themselves speak of the Void in mere fragments- focusing on the warnings.
"To seek the Void is to pluck the string that was never meant to sound," one Grand Elder once said.
"It will not answer. It will unmake the question."
The Void has no laws - no resonance, no structure, no passage of time or thought. The Vortigaunts believe all things that exist are bound by the Great Weave - the harmonies of motion, purpose, and connection. But the Void lies outside this. Not by design, but by consequence. It is the result of something lost, something severed from the universal thread.
The Elders teach that even the Combine, with their dimension-rending technology and hunger for control, have not touched the Void - or if they have, they were wise enough to turn away. For to observe it is to risk forgetting yourself. Not death. Not madness. Forgetting. A dissolution of identity so total that even the Vortessence cannot retrieve it.
For this reason, the Void is treated among the Vortigaunts not as an object of study, but as a sacred unknown. It is spoken of in parable, in meditation, in the quiet chants of mourning. Some say it is where the lost go - those who perish far from kin, whose resonance is severed without closure. Others say the Void is a warning left behind by a species far older than any known, whose fate was to become nothing at all.
Whether metaphor, myth, or truth, the Void remains untouched. And so it must stay.
"The Void is not an enemy, not a force, not a place. It is the space between the song.
And to touch it… is to silence your own verse."

History of the Borderworld "Xen"
To most people, the idea of the existence of the Borderworld is on the lines of Science Fiction, however, after the Black Mesa Incident, its subsequent portal storms and the Seven Hour War; it is far more than general expectation and fact that the Borderworlds do indeed exist. As for how many there are, if all universes have them and if its just a unique feature to a select few universes is majorly unknown- but its existence proves clearly that multi-verse theory that was long believed as interesting myth is now undeniable fact.
Among the many worlds discovered by humanity, none is more infamous than Xen.
Xen is a Borderworld, a dimensional crossroads that exists between a few universes and realities. Rather than being a conventional planet, Xen is composed of vast floating landmasses suspended within an almost endless void. Its terrain is fragmented and often unstable, with entire ecosystems existing upon isolated islands separated by immense distances. Despite its hostile appearance, Xen supports a wide variety of alien flora and fauna, many of which would later appear on Earth following the Black Mesa Incident.
Long before Humanity discovered Xen, it had become the refuge to a powerful being known as the Nihilanth. Having fled from the Combine, the Nihilanth established itself within the Borderworld and gradually transformed Xen into the center of a growing empire. Numerous species became trapped within its domain, either arriving naturally through dimensional displacement or being forcibly relocated by the Nihilanth's forces.
Amongst these species were the Vortigaunts, who would later become one of the most important races in modern human history. Through a combination of advanced technology and biological manipulation, the Nihilanth enslaved much of the Vortigaunt population and used them as laborer's, soldiers and servants throughout Xen. Other creatures familiar to Humanity; including Headcrabs, Houndeyes, Bullsquids and countless other lifeforms also came to inhabit the Borderworld during this period.
Humanity's first direct contact with Xen occurred during the Black Mesa Incident. The Resonance Cascade weakened the barriers separating Earth and the Borderworld, allowing Xenian organisms to cross into human-controlled territory leading to an Xenian invasion within the borders of the United States. In response, Black Mesa's Lambda facility was later able to open their own gateway into Xen, culminating in the death of the Nihilanth at the hands of an individual later identified as Gordon Freeman.
The consequences of the Nihilanth's death were immediate. Its empire collapsed, its armies fragmented, and the Vortigaunts were freed from centuries of enslavement. For a brief period, Xen existed without a dominant power for the first time in generations. Despite this newfound freedom, the consequences of the Resonance Cascade continued to reshape both worlds. Throughout the four-year Portal Storm Crisis, countless Xenian lifeforms, plant species, and even entire fragments of Xen's ecosystems were deposited upon Earth as unstable dimensional breaches continued to link the two worlds together.
This period of freedom proved short-lived.
Following the arrival of the Combine, Xen became another target of their expansion. The Borderworld's strategic position between dimensions made it far too valuable to ignore. Over time, Combine forces established control over large portions of Xen, forcing many surviving inhabitants into hiding while others fled to worlds beyond Combine reach.
Today, Xen remains one of the least understood locations known to humanity. Much of its vast expanse remains unexplored, its ecosystems poorly documented, and its current political landscape largely unknown. What is known is that Xen continues to serve as a gateway between worlds; and as a reminder of the events that first brought humanity into contact with forces far beyond its understanding.