The dimension known as Xen is a 'border world' between other more or less conventional dimensions along side those which may seem completely foreign in nature. The world itself is a shattered, floating-island-like place very much akin to the Shadow Shard accessible from Paragon. The world has its own history, a very long one, and it is directly tied to Keenan's. As it exists [in the Half Life universe] in a sort of parallel to Earth, it can be used to 'slingshot' Earth-bound teleportation from one spot on Earth to another, where moving directly (earth to earth locales) is extremely difficult. By placing a sort of marker on this other dimension, it becomes far easier to then redirect to another plotted spot elsewhere. The 'Lambda Teleporter' in the Black Mesa Research Facility is tuned to use these markers, and while the exits are often mundane spots (like Hoyle's enclave, the Icarus facility, and Wilson's physical home) it has been also used to explore the world of Xen itself.

The Vortigaunt Hive - tucked away inside the semi-natural hollows of the Xenian islands are numerous collections of Vortigaunts. While they had been enslaved for thousands of years, they were freed by the actions of 'The One Free Man', Gordon Freeman, and sadly at the same time his actions all but condemned their kind to extinction. This particular hive includes Noah's sleeping spot hidden at the top, and some stray Pantheon members who find the Xenian landscape to be more intriguing than their home world.

The Nihilanth's Chamber - though the creature itself is dead, its horrific remains still fill the egg-shaped interior of this large floating island. Described by Freeman as 'that floating, explody-head baby-thing' and that's almost precisely what Nihilanth looked like. Though distantly related to the Vortigaunts, it was known to be the last of its kind, and thankfully its kind are now fully extinct. It was, as Keenan is apt to sigh, one of the creatures that he had made deals with in order to take down Ulathoi - it was a gamble that he lost. Nihilanth was meant to be a spy among Ulathoi's ranks, but it wound up instead fleeing Ulathoi's control, and almost led them to the Vortigaunt homeworld. To keep that from happening, Noah and Nach'lih kallah-vahh made a deal - one which most Vortigaunts are still a touch bitter about, as it enslaved them, but brought them to the relative safety of Xen, where they spent the next ten thousand years.

Much of Xen can be explored carefully. There are numerous chambers, nooks, grottos and islands that sport unusual wildlife and beautiful sights. However, that unusual wildlife often is hungry... The glowing Xenian crystals hum with a Vortal energy, and are what Black Mesa uses to focus their teleportation devices. The pure sample of one which led to the 'Events' - the Resonance Cascade in Black Mesa, and the Synchronicity Event in the Enrichment Center - had been taken (by Keenan) from Nihilanth's chamber itself. The floating 'controllers' may shoot fireballs at you, houndeyes bark and use a pack to hunt, headcrabs by the thousand are spurted out from Gonarch-level 'mothers'. Like I said: carefully explore, and you might live to tell the tale.

Keenan Lane's Office - though the entry of this office is shrouded in darkness and is available through the 'Hub' it should be considered a Black Mesa area. The office itself has no doors, and is entirely created Vortally. (And thus, also should be considered Sanctuary, again I didn't feel like adding so many colors to the map.) The office is dark, underlit, and at the business end of it has a wide (supposed to be black marble) desk. Behind and to the sides of that desk are large, almost full-wall size 'windows'. Those windows show an unusual landscape: Xen, or whatever Keenan feels like showing in them. The office doesn't exist anywhere physically so they overlook places that he's been, the images in his mind, or nothing at all, at his whim.

Keenan keeps mementos here, awards from his investments in companies such as Aperture or Black Mesa, Rapture, and more modern trophies gained from his life in Paragon. He does not display these things, having seen that they are apt to make their owners seem a bit too arrogant. He also has a good stock of liquor, wines and occasional beers here, but Mars and Wilson continue to raid them - at some point, he'll have to actually find more.