After arriving on Xen, Calhoun starts his journey towards the relay device that's required to get the old prototype teleporter lab working. Along with fighting through the many alien creatures of Xen, Calhoun traverses through many notable areas, such as a maze of small tunnels, floating rock platforms, and a flowing river, until eventually reaching the location of the relay device. Said device appears as a machine housing one of Xen's large orange crystals, which Calhoun turns on said machine, and then turns the knobs on the relay computer towards the best focus in order to connect the relay back to Black Mesa. Once the relay is set, Calhoun fights his way back to the location where he was first teleported to Xen, which sure enough, a newly created portal is seen. Dr. Rosenberg can be heard on the other side ordering Calhoun to enter it before the portal closes, which Calhoun does so.
Calhoun is teleported back to Black Mesa's old teleporter lab, which Rosenberg congratulates the former for a job well done now that they have connection to the relay. However, Rosenberg provides the bad news that Calhoun's trip to Xen ended up draining what remained of their power supply to run the old portal chamber. Thus, a new power cell will be required in order to have enough energy to create a teleport exit that will last long enough to get them all out of Black Mesa. Rosenberg informs Calhoun that he sent a couple colleagues down to the prototype teleporter lab's lower level to retrieve a new power cell, but he hasn't heard from them since. Given that Calhoun is the best equipped to deal with whatever dangers his colleagues may have run into, Rosenberg brings him over to the elevator to the lower level. Rosenberg explains that the lower level houses the old power generators for the prototype lab, and that along with Calhoun needing to find a new power cell, he will have to charge the cell up before sending it up to the lab. Calhoun then takes the elevator down to the prototype lab's lower level.
This Chapter contains examples of:
- Alien Landmass: For one chapter, Calhoun traverses through a section of the alien borderworld, Xen.
- Drought Level of Doom: Xen can be this, as there are no armor pickups anywhere (which makes sense, as the HEV-wearing expedition teams would have had no reason to bring any, since there's no reason for a security guard to be on Xen) and ammo is relatively spaced apart and only found on dead expedition team members, who usually only carry about a mag each for your basic weapons. On the plus side, the healing pools provide infinite health regeneration. Going in with full armor and ammo is very helpful.
- Floating Platforms: Given that it's Xen, part of traversing the level is made up of jumping across these.
- Multicultural Alien Planet: A bit more world-building for Xen is seen here. The flowing river especially gives the Xen borderworld a more naturesk habitat feel to it.
- Road Block: You can't head for the teleporter that takes you back to Black Mesa until you fully activate the relay device.
- Secret Room: The "Chumtoad's Lair."
- Sidetrack Bonus:
- There's a lot of side areas on Xen that provide extra supplies left behind by dead members of the Black Mesa survey team, especially in the maze portion that has you crawling through small tunnels.
- At the end of the maze tunnel section is a deep pond. Swimming to the near bottom has a hidden path that leads into the secret "Chumtoad's Lair," which are small harmless alien toads. It's also one of only two locations in the game where Calhoun can obtain Snark ammo.
