To your right, you can find an HEV charger and a health station. To the left is a door leading to the Lambda Core teleportation chamber, with Freeman running into the teleporter. The gate will fail, and the scientist on top will be killed. You aren't trapped, but you are provided with an alternate teleport that you should use instead.
You will arrive at Xen, where you will need to jump across platforms. After jumping across the first two, another scientist has teleports in and hits the ground, dropping the Displacer-Self weapon. Collect it. If desired, you can use it to visit part of the Black Mesa training course, and collect a few items of interest.
After the scientist's platform, jump to the next one, where there is a jump pad. Instead of continuing straight forward, use it to reach one of the platforms in the middle.
The final platform has two hound eyes, which may be ignored if you are quick. Use the final launch pad to reach the platform next to the teleport point, and jump directly into the teleport. If desired, you can take a dangerous shortcut by using the launch pad to reach the teleporter directly.
- The displacer-self places you at a generic Xen location containing HEV charge packs.
When the elevator stops, take a right turn. The scientist will ask you to rescue him by activating the console (where two pit drones are hiding.) When he is released, have him follow you and open the first door.
Although the scientists will try to open the next door for you, an electric shock will stop him. Instead, you will need to look in one of the shattered tanks, and climb up. This leads to some air vents, which are dark, and contain Pit Drones.
At the end of the ducts, you will reach a teleport station.
- The displacer-self malfunctions when used to teleport.
You should reach the teleport room. Activate it, but it will malfunction for a few seconds first. Once you reappear in the water, look up for an exit. Kill all zombies in the path, and break open a grate at the end. This should land you into another aquarium.
On approach to the control room, there are two zombies (one of which is fast), and a headcrab. There are two more zombies in the room where you do your work. Climb down and turn the wheel to open the exit path. With the path open, you can recharge. While the med station will explode if you approach, you can still use the HEV charger to regain armor.
Dive back into the water and follow the newly opened passage to reach the airlock. If the monster is in the corridor, swim past it as quickly as possible.
- The displacer-self teleports you to a Zen border world where you can collect some items. Collecting everything requires two charges of the device, but it is only cost effective to visit the place once. If used at the start of this region, you could skip some of the map.
The doors open to an X-ray system. You can't use the button to turn it off, but you can walk to the left, and shoot the fuse box to cut the electric power. This allows you to proceed, where you encounter a pit drone and a shock trooper. Proceed through the doors and into the airlocks into the underwater sections.
In the first corridor, you should see a teleport entrance, which transports you to Xen. This is a short jump that overlooks the other floating platforms that you could access by the displacer-self.
In the final aquarium corridor, the metal catwalk is broken. Dive into the water, and swim into the chamber. Head directly to the exit visible at the top of the aquarium and escape.