The trip through the portal leaves you in a small room, and when you open the door, you see a room being scanned by a camera. In the only choice in the game, you get to choose the upper or lower path.
Lower path[edit]
The lower path is quicker, but you lose out on the secret room and collectible artefact.
As you can see, the camera is scanning the ground floor. When you are detected by the camera, it will release gas that will slightly injure you. This path is easier if you take out the camera, but it is not necessary. To cut the camera's power, look for a fuse box on the far end of the level. Pickup a rock on the ground (or a book in the first room), and throw it at the fuse box to break it open. Throw the book at the wire again to cut the power.
At the first end of the corridor, you will find a metal crate, and a 10-second button. Press the 10 second button, and push the crate through the door at the end of the corridor. If 10 seconds expire, or if the camera triggers, the door will close. Behind the door is a pressure plate, where you will place the crate, and enter the next room.
Upper path[edit]
The upper path is more difficult, as it requires objects. It is inaccessible as soon as you approach the lower doorway.
In the camera room, the sole objective is to reach the door at the far end of the corridor. It can be reached by jumping across the broken pillars, despite the jumps being unreliable. If you fall down, you head to the button, climb the crate and wall, and jump back on one of the pillars.
There are two metal beams that can be placed across the pillars. The first is located in the starting room, and the second is just left of the first door. The beams will snap into position as soon as they're close to the pillars, although other paths exist and may be used instead.
When you pass through the door, it will close behind you and water will start pouring in the room. To escape, you need to find three boxes in hidden panels within the walls - the panels will slide open, and you can pull the box out. These boxes need to be placed in the corners so that they will touch the pressure plates on the ceiling. Only three boxes are technically required as long as you ensure that all four plates are being touched. When all four are pressed, the water will drain from the room, and you will enter the cafeteria.
Secret room[edit]
After completing the upper path, you can access the secret room in the cafeteria.
On the right, you can find a door which you can open for some boxes. Stack these boxes beneath a vent, and enter. This leads to a small room with the artefact, and a computer that can disable laser security. You may also clear other items from the desk to get a new icon in the computer. If you complete the game, you will receive a password that lets you listen to the recording.
Password: ikj765
Cafeteria[edit]
On one of the tables, you will find a cassette player. It will suffer from an repetitive audio glitch, despite having no tape inside. Get a replacement tape from the vending machine, and place it in the player. This unblocks the door, as well as places a few crates.
Push one crate through the door, where you will see a laser hallway. If these lasers weren't disabled in the secret room, they will blink on and off. They don't react to the crate, but if you pass through them, it will detonate the nearby explosives. Push the crate through the hallway, collect the portal key within the corridor, and place the crate on the pressure plate.
You can now go through the door. Pick up the radio twice to get access to the moving platforms.
Platform room[edit]
Before the portal is a room with moving platforms and crates, as well as the portal key.
You first need to reach the portal key. Jump onto the platform on the left, to eventually reach the platform heading up and down. Jump to the platform that heads closer to the portal key, where you can climb down the ladder. Take the key, and return to the corner platform.
With both keys, you may jump across to the other end of the room, and enter the portal.