"Gordon didn’t know where he was. A fresh breeze flowed across the face, and the air… the air was ideally clean and fresh, filling the exhausted lungs with strength and life.
Freeman closed his eyes, then opened them sharply. And I saw nothing except this fabulous, extraordinary beauty of distant space – the twilight sky, shimmering in purple and turquoise tones, on which sparkling stars played. But the sky somehow changed, a greenish tint was added"
(Markov Vladislav. "Half Life")

Zen is a link between worlds. The connecting knot of the Universes. A place of extraordinary beauty and cruelty. Here danger lurks at every turn. Here everything is turned against you. It’s easy to go crazy here. It’s easy to die here. Zen is a place that people call Purgatory.

Zen, in my opinion, is one of the most interesting parallel worlds that has been created in the history of computer games. VALVe managed to create a world of unprecedented beauty, where you can gaze at the falling necklace of stars, and then fall dead from a monster jumping up from behind.
As already mentioned, Zen is a kind of Purgatory. Yes it is. And besides, Zen is the so-called “border world”. Why? I will answer this question a little later, now we need to figure out what it is – Zen.

Xen existed long before the arrival of the Nihilanth with the Vort race. You could say that Zen is eternity. Canon – “was, is and will exist”. But here is one of the ledges that is so easy to run into – if Zen phenomena are eternal, then where are the teleport cabins between spaces from?? The most interesting thing is that these cabins are made with skill, nature (in our understanding) could not do this. What lies behind this? Having built a certain line of meaning, we can assume that Zen is far from being a product of the independent activity of the Universe. Someone (by no means “something”) created Zen on purpose.

The structure of Zen is a chaotic https://nongamstop-casinos.uk/ collection of various “levels-spaces” connected to each other, as mentioned above, by special teleport cabins. Once you enter one of them, you don’t know where you’ll find yourself in the next moment. Each "space" consists of "islands" that float in the vacuum of space. One big one, the main one, and others, smaller ones, which, as if in an orbit, revolve around it.

In Half-Life, everyone saw that Nihilanth was in some strange room that does not resemble the “Xen” structure. Most likely, Nihilanth was in a special room built for himself, so that no one would be able to find him so easily. There is a version that Nihilanth was not in Zen, but was in another Universe, the path to which lay through Zen.

Zen also has its own flora (tentacles) and fauna (headcrabs, bullsquids, houndeyes, ichthyosaurs, it is possible that also antlions, barnacles, gonarchi) which, apparently, have intelligence. And not the weakest.

So, the main question is why Zen is a “border world”? Every race, every being that teleports through something called Xen, the "border world". It’s not for nothing that Judith Mossman used the words “Zen resonator” and “Zen relay” in Half-Life 2, hinting that people continue to use Zen space for teleportation. It’s comprehensive. You can get from one point to a completely different one through Zen. The problem is that Zen himself will decide for you whether to move further or not, by arranging tests. As seen in Half-Life, Opposing Force and Blue Shift, you have to stay alive while you get to the next teleport booth.

“Only now I realized where I am – Zen.
I was presented with the most, most beautiful landscape I have ever seen. It seemed unattainable, something people have been striving for for thousands of years. It was… lovely, wonderful. A green-violet endless mess, with a necklace of stars, nebulae and galaxies scattered on it. And the sun. So small, it seems distant, but so… dear.
I looked down. Everything was like on a mirror, the sky was reflected in emptiness, the same galaxies, the same nebulae, the same stars, and the same sun.
Stepping back I smiled.
It’s a pity that I saw such beauty for the last time. She was hostile, like me – an uninvited guest who does not fit into such a landscape in which dreams and hopes come to life, the soul takes wings, the body falls to the ground like long-forgotten clothes, and you… fly, soar in flight, spin next to stars and planets, dive into galaxies and swim in nebulae.
Rivers of stars.
Mirror of suns.
Galaxies and nebulae.
Is it really here, right here, in paradise, that hell lurks, slowly opening its predatory mouth?
(Markov Vladislav. "Half Life")

The most important feature of Xen as a “border world” is that there are absolute conditions for the survival of absolutely any species. There is an atmosphere here like on Earth. You can breathe. Water like on Earth. You can drink. That is, you can survive. Basic life instincts are suppressed. Then you continue – you decide: to survive or not.

It’s interesting that Zen is a living world that can be merciful or cruel towards you. It can heal, it can kill.

Due to the fact that Nihilanth ended up on Xena, this world became the object of the acquisition of two forces. One, to which G-man belonged (hereinafter referred to as the Organization), the second – the Alliance. Soon a third force appeared – Earth. The organization decided to take a risky step – to provoke an invasion of Xen through the Earth, thereby giving rise to the capture of this world and the destruction of Nihilanth. The Alliance had no choice but to watch everything that was happening.

Who created Zen, for what purpose?? And why did the Organization need him?? These questions may be answered by Half-Life 2: Episode Three, if not Half-Life 3.