One of the commentary nodes by a Portal 2 developer, Eric Tams, said they used "world portals" to quickly reconfigure maps and puzzles during testing, which allowed them to create rooms that were bigger on the inside, infinite falls, and other sorts of impossible geometry, save for the users own ASHPD space bending.

When we started the project, making any big structural change in a level or the order of levels would lead to hours or even days of busy work trying to reconnect things and make sure they lined up again. If we ever wanted to ship something the size of Portal with the finely tuned balance we desired then we needed a way to be able to make big changes to the layout of the game without paying the cost of making everything line up again. We needed a way to bend space.


Soon every connection between any space was a portal. We would even switch them on the fly. Even a simple door worked like the cartoons - just a facade painted on a wall that seamlessly opened somewhere else entirely. Once the game settled down we were able to finalize our path and remove all of the world portals. There's only one impossible space left in the whole game. See if you can figure out where it is.

After the map layout was finalized, most of these were fixed into boring linear spaces, likely for the sake of performance, save for one spot. Where is it?

  • 38
    Very interesting, I didn't know about this! +1 since I'm super curious if this is true and hidden somewhere in the game!
    – chandsie
    Commented Apr 22, 2011 at 0:55
  • Fun Fact: Something similar was used here and there in American McGees Alice. F.e. an iron gate in a wall. From one side it was a normal iron gate, from the other it was a gate (with no iron bars) to a room.
    – Bobby
    Commented Apr 23, 2011 at 13:09
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    This doesn't have to do with levels, but Wheatley's eyelid is "impossible". In order for it to fully open and shut, it would be too big to fit behind the inner-most ring around his eye. The developers wanted the core to look mechanically plausible, but they ignored the geometry to produce a more expressive character.
    – Nick T
    Commented Apr 30, 2011 at 16:46
  • They did this in the original Unreal more blatently, where there was a portal you could see and walk through, the exit was simple a stone slab you could walk 360 degrees around. I thought it was pretty cool.
    – NibblyPig
    Commented Mar 14, 2012 at 16:23

9 Answers 9



In the entity list, there is a linked_portal_door for this purpose; it is used in the Death Trap (in map sp_a4_finale2.bsp):

This entity is designed to link two separate, distant areas together without any clear transition between the two. This entity is exclusive to Portal 2.

It is used in Chapter 9, in the Chamber 75 Death Trap with all the crap turrets. The room is actually completely separate from its supposed surroundings. It is the only use of this entity in the final version of the game, though commentary states that it was used a lot during the development of the title to link chambers together.

I guess that the development team first made the rooms separate so that they could wipe a bad room, then connect them later when the levels were more perfect, and I suppose that this room didn't fit.


Here is a picture of the Death Trap that isn't connected to the other rooms:

alternate view

Near the threshold and a tiny step (noclip fly) to either side:


You might want to skip the commentary and long walk and go to 04:30. From here on he shows the box from outside at the three locations (before box, in box, after box); he first does this slowly, then at a later point he goes between all of them in quicker succession. This might show the trick better than above pictures.

Thanks to Jon Ericson in the comments for finding this video.

  • I really don't get it. Why they HAD to use a portal door? The room is not really that bigger! I have two theories: 1-It's because of the exit door placement or 2-They wanted to avoid moving 6 physical entities in real-time (the turrets). I hope we'll find out the real answer someday!
    – Hilydrow
    Commented Apr 24, 2011 at 18:48
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    @Hilydrow It's because of the lighting. If the entire room itself moved, they'd have to have used dynamic lights which are calculated on the fly, rather than before hand, which makes them much slower.
    – user56
    Commented Aug 22, 2011 at 19:07

That does make sense in The Part Where He Kills You, but they had to put that in because the room was moving.

There was one in chapter 4 when you escape from Glados light bridge experiment. I wanna say it's test chamber 22. Anyway, once the lights turn off, you are in a different and similar room. It doesn't make too much sense to duplicate the room cause they didn't have to.

Anyway here is the part where Wheatley comes to save you:

enter image description here

You can see two distinct test chamber rooms. The test chamber one with the entrance that you came in from:

entrance room

You'll notice that the rest of the level is missing from this room. It should extend from the near right side.

Then there is a completely different one that is missing an entrance that connects to the escape from Glados.

escape room

And here is a shot that shows both the rooms in the same load from the escape side.

both rooms from the escape side

And from the entrance side

Both rooms from the entrance side

What is interesting about this isn't that they did it, it's why they did it. As far as I can tell, there was no reason to other than because they could or because this is what they left in for us to find.

However, I totally agree with the death trap theory. I checked that out and they stuck that turret room somewhere else. They couldn't use the room that moved because of all the destructive animation they had just done on the left side of the room. If you watch that room crash into the wall, you'll see a lot of stuff deforming inwards which would have poked through to the turret room.

I have to say though, after searching around the game for this, the level designers did an awesome job of placing everything together in a linear fashion. There as some levels I was sure wouldn't work out, but they crammed it all together quite nicely when you look at it.

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    This is an interesting map feature as well, what seems to happen is that you enter the map (sp_a2_bts1.bsp) into the small part of the map, then it teleports you to the other part. This transparent teleporting could also generate "impossible geometry", but I'm not 100% sure if there effectively is any (not that there was with the other `:`)
    – Nick T
    Commented Apr 24, 2011 at 3:41
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    They did duplicate the room. Somewhere along the hard light bridge is a trigger that teleports you to the other room, without light. Commented Dec 16, 2017 at 19:28

My guess is


The distance between

Moon and Earth

doesn't seem to have been conserved.

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    The connection between the "rooms" is only made with the ASHPD though, which I don't think counts
    – Nick T
    Commented Apr 22, 2011 at 11:52
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    Actually looking at the map with noclip, it's just a hole in the floor. Your own portals probably aren't.
    – Nick T
    Commented Apr 22, 2011 at 12:00
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    Well then it still is "impossible space" :) @mana : Thanks for the edit, I didn't know how to spoiler. Commented Apr 22, 2011 at 12:20
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    Hey yeah, we shouldn't have seen that twinkle on the moon until like 2.6 seconds after firing! And that's assuming that a hot ball of portal flies at the speed of light.
    – Dan Ross
    Commented Jan 20, 2017 at 22:50
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    @DanRoss It does take 2.6 seconds before the twinkle of light, I just played through. Commented Dec 17, 2017 at 2:47

Possibly the long fall after Wheatley knocks GLaDOS and Chell through the floor is an example of the infinite fall they mention?

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    It's a changing environment, though. As far as I can tell, the pipes and things don't repeat.
    – Maxpm
    Commented Apr 22, 2011 at 6:43
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    It could be changed with some minor additions, but an infinite-fall impossible geometry seems like a somewhat banal use. I can't no-clip it to see, it won't let you move on that map.
    – Nick T
    Commented Apr 22, 2011 at 11:29
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    Doesn't the game stop and load a new map specifically for the fall? I don't think this answer is correct. Commented Apr 22, 2011 at 17:35
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    @Blue, yes, sp_a3_00.bsp consists purely of falling, where you are unable to move, even if you noclip.
    – Nick T
    Commented Apr 22, 2011 at 19:45
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    You're not even moving, a tube just moves up around you Commented Dec 17, 2017 at 2:59

I have been looking around the other forums and one guy said he no-clipped (flew through the walls) to look for it and he thinks it is the incineration tube that Glados drops you down right after you wake her up, and I agree.

I just played that part again and just after you find her still dead you walk behind her, jump down those broken stairs, walk over some cat walks and are now under Glados. If you look around you can't see the shaft that leads to the incinerator in witch you will soon be falling. I think they may have made that into an infinite fall.

  • See comments to @Martin's answer, I don't think this is correct. Commented Apr 22, 2011 at 20:47
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    This is incorrect. sp_a2_intro does not need an "infinite fall", as the map really is that tall, and nothing else sticks out as requiring a world portal.
    – Nick T
    Commented Apr 23, 2011 at 15:56

It could be that they used square portals to go from place to place? In youtube videos there are square portals(I have xbox version so I dont know the codes) and they could have put only the door frame. And I am refering to the first Wheatly test and the room with the exit door that was too big by the way.


I believe it's the

Moon and Earth.

When you fire the portal gun, the first portal will change its color according to which portal you launch. For example, if the first was orange and you launch a orange the first one turns blue. The distance between the two places changes; when you're on the far side, you're closer.

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    That's not true. You don't get to decide which colours your portals are. The one in Aperture Science is orange, the one on the moon is blue.
    – user56
    Commented Apr 26, 2011 at 5:18
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    No, you can't, but it doesn't matter which portal you shoot, it always ends up orange on Earth and blue on the Moon; there's one more place where it doesn't matter which one you shoot: where Wheatley tries to kill you with the spikeplates and you are inside the beam thing, if you shoot wrong portal, they just switch the original portal under the source of the beam.
    – miiz
    Commented Sep 8, 2011 at 7:36
  • That's not impossible space, though. Also, not the only place in the game where your portals can get swapped, but that's for gameplay purposes.
    – a cat
    Commented Nov 8, 2011 at 17:57

The impossible space is one of the test spheres. Before you enter it you can clearly see how big the exterior of it is, yet once you are inside of it you can now clearly see that the interior of the sphere cannot fit within the boundary of the exterior.

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    It actually changes levels in most of the enrichment spheres, so it doesn't use the impossible space mechanic but it loads a new level. In my opinion, the enrichment spheres do actually fit the levels inside them properly, but that's just my judgement Commented Dec 17, 2017 at 3:04

I think that it's the one room where Wheatley makes his first test. When you complete it, and go through the door, then he wants you to solve the same test again, then 2 panels open and you walk through, and you are at the beginning again, but the distance between these spots is actually huge and you can see it doesn't make sense at all.

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    Not true at all. Made me check, though.
    – a cat
    Commented Sep 10, 2011 at 10:21

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