Skip to content
Part 20
Portal

Part 20

Complete Portal Part 20 walkthrough, including Companion Cube incineration, Test Chamber 18, and GLaDOS's cake quote.

By ···10 min read·Multi-source verified
1 reading this guide  

Complete Portal Part 20 walkthrough, including Companion Cube incineration, Test Chamber 18, and GLaDOS's cake quote.

Walkthrough
  1. 1
    Listen to the Enrichment Center's message about the Companion Cube.
  2. 2
    The computer states testing cannot continue until your Companion Cube has been incinerated.
  3. 3
    The computer explains that eight out of ten Aperture Science engineers believe the Companion Cube is incapable of feeling much pain and that regulations prohibit it from remaining alone. You must euthanize it.
  4. 4
    Destroy your Companion Cube or testing cannot continue.
  5. 5
    Leave the cube on the button, then go down the stairs.
  6. 6
    Once down the stairs, look towards the large grey cylinder coming out of the floor to your right.
  7. 7
    Go into the small room on the side and press the button.
  8. 8
    Run back to the cube, bring it over to the incinerator, and throw it in.
  9. 9
    The computer congratulates you on euthanizing your faithful Companion Cube more quickly than any test subject on record.
  10. 10
    Turn around and enter the chamberlock.
  11. 11
    Run onto the small piece of land ahead in Test Chamber 18.
  12. 12
    The computer states the experiment is nearing its conclusion and reminds you that you will be baked and then there will be cake.
  13. 13
    Look to the left to see the panel.
  14. 14
    Look across the gap, then up at the ceiling to see white wall.
  15. 15
    Shoot a portal there and at your feet.
  16. 16
    Turn left to see a piece of the wall that is broken.
  17. 17
    Crouch down and go through the broken wall.
  18. 18
    Once inside, look to the right to see it floating behind some boxes.
  19. 19
    Head out of this area.
  20. 20
    Shoot a portal at the white wall in front of you and the other at the ceiling above the platform in front of you.
  21. 21
    Jump through. Be careful not to jump in the water.
  22. 22
    Once in, aim yourself away from the corner that is not there.
  23. 23
    Face the pistons and shoot a portal at the ceiling above them.
  24. 24
    Then shoot a portal at your feet.
  25. 25
    Look to the right of the dividing wall.

Commentary Nodes:

  • Located down the stairs, to the right of the large grey cylinder coming out of the floor. Features commentary from Jepp Barnett on the dual purpose of the Companion Cube's incineration.
  • Floating on the small platform in Test Chamber 18. Features commentary from Eric Wolpaw on the AI voice creation process.
  • Inside the area behind the broken wall. Features commentary from Ellen McClane, the voice of GLaDOS, on acting direction.
Tips
  • The incineration of the Companion Cube serves as training for using the incinerator in the final level.
  • The AI voice acting process involved text-to-speech, mimicry by Ellen McClane, and post-processing for a computery edge.
  • Ellen McClane received specific direction like "explosively indignant" which she found helpful.
  • Be careful when jumping through portals after Test Chamber 18 to avoid falling into the water.

100% Human-Written. AI Fact-Checked. Community Verified. Learn how AntMag verifies content