Dr. Horn's Xen Lair

There is a hidden cave in Xen where evidence of Dr. Horn's presence can be found. A mysterious gate, a whiteboard with Dr. Horn's writings, a radio with a message, pizzas, Dr. Horn's and Dr. Welsh's nameplates, field lab equipment and excavation equipment are among the things that can be found in the cave. The cave is located in the first map of Gonarch's lair. One of the whiteboards in Xen there is a reference to a mysterious gate in Site 8-B, which most likely is referring to the gate found in this cave.

Dr. Horn's Xen Lair

Getting there

After the first Gonarch fight, locate this area and look for a purple plant on a ledge.

Climb up to the ledge with the purple plant and walk towards the "The Pizza is a LIE!" graffiti.

You will be teleported into this crystal cave with a visible teleport. Enter the teleport...

...and you will be teleported into a small cave with a tunnel leading to the "lair".

See the video and the image gallery above for how to get to the lair.

Alternatively, one can get there by typing the following commands into the console:

map bm_c4a2a
sv_cheats 1
noclip
setpos 7360.489258 11451.112305 1058.586548;setang -2.640002 82.147278 0.000000
noclip

Image gallery

The lair viewed from the cave entrance.

Field lab equipment.

A radio with a message.

The "conspiracy" whiteboard.

Two HEV suits with Dr. Horn's nameplates on both suits.

A mysterious gate.

A rare specimen?

The gate viewed in model viewer.

Transcript of radio message

*BEEP*
—Miller, you're never gonna believe who i just ran into today. DR. HORN. I couldn't believe it. I thought that guy had vanished off the face of the planet. I mean, he keeps himself cooped up in those labs all day long. Sure as hell hope they have a shower in there or something, cuz good lord does he need it. Anyway, we got to talkin' durin' our lunch break. Apparently, the good doctor's gettin' ready to file some complaints against multiple people, one of which being security officer Sisk! Now, you got my performance review on Sisk, and I gave that guy top marks, so, sufficing to say I was a bit put off by it. But I decided to play along, and I said, "Well, Dr. Horn, what seems to be the problem?" And that's... when things got really weird. He seems to think that everyone in his department—AND security officer Sisk—is going behind his back and stealing his slices of pizza. One by one. Out from under him when he's not looking. Says it's their way of taunting him or something. Then he goes on about saying how he thinks some of the other doctors on his team are trying to break into the labs that he and, uh... Dr. Junek... only have access to. He's even said that he's gone as far as putting down fingerprint-lifting powder to catch them by trying to match their prints. I s#!t you not. That's what he said. Honestly, sir, I... did not know how to respond at first. I mean, normally I would have been all witty and sarcastic-like, but this was a whole new level of weird that I just wasn't prepared for, especially with this guy, so... so I asked him, "Do you have any proof?" He just looked at me, straight in the eye, and said, "I can smell the pepperoni on their breath." Then he turned around and walked away. So... I think that guy has been cooped up in that lab for too long. That's my official stance on this. He has got the cabin fever and he is owning it like a boss.
—Hey Calhoun! Guess who just locked himself out of his office again?
—Aww, not Kleiner!
—Yup. Guess who's in the vents?
*Recorder falls*
—Ah- he's already halfway there. You ain't gonna beat him.
—Bullshit!
*Other officer picks up recorder*
—He ain't gonna beat him.
*Transmission ends*

Based on transcript by DUMBin8er.

Leaving the cave

"Using" the laptop will cause a teleport to appear behind the desk near the cave wall, which leads back to a location outside.