Catwalk it is, then. With a few fairly impressive feats of acrobatics, she vaults herself into and out of a portal and manages to land on a catwalk.

And she runs.

The catwalk is in good repair, straight, and makes a great running track except for all the clatter and shake from her footsteps. The tubes become less gratuitously tangled and start paralleling the catwalk, assorted objects flashing by in the opposite direction.

Actually, they're not assorted, they're all Weighted Storage Cubes.

...uh huh. This is suspicious and interesting. She'll keep going and see what she reaches.

The surroundings have resolved into two parallel arrays of straight vertical tubes. Above, robot arms are taking Weighted Storage Cubes from some sort of pair of slow conveyor lines passing overhead, pausing to do something, and then dropping them into the tubes.

As she climbs up to the level of the conveyors, she can see more of what is going on. The robot arms are dexterously removing the Weighted Storage Cubes from a line of Weighted Storage Cube Storage Pallets, performing some subtle manipulation causing them to pop open, tipping them out onto the second conveyor (a mining-style conveyor belt suitable for loose material) — which causes nothing whatsoever to fall out — closing them up again, and dropping them in the tubes.

...the cubes are hollow? Why are the cubes hollow. Why are they being emptied of literally nothing. Why all of this.

She'll move on carefully, watching her surroundings.

The routes from here are back down to the spaghetti plumbing, or alongside the conveyor belt. The best approximation to further in the direction she is going is the direction the Weighted Storage Cube Storage Pallets are coming from.

The catwalks also allow access to various parts of this mechanism, if she would like to examine or sabotage it.

She has no reason to sabotage the machines, cubes are nice, they're about the least objectionable aspect of this whole facility.

What she wants is out. She doesn't know for sure that the whoever-it-was isn't still monitoring her but unless they have more capabilities than GLaDOS did she should be fine for now. She'll keep going forward, out, and up. The direction the cubes are coming from seems as good as any.

After another long walk — these catwalks are evidently part of the Aperture Science equivalent of a building code, because no human would put them in for their own purposes instead of, like, some sort of transit system — she finds that the pallets of cubes are emerging from a doorway in a large concrete-walled warehouse (supported on columns rising from the misty depths, of course).

The catwalks allow access to a human-sized door into the building, which proclaims that this is the Weighted Storage Cube Storage Pallet Storage Vault. They also extend left and right; the view is blocked by assorted large objects, but there are sounds of active machinery all around.

Why, it stores Weighted Storage Cube Storage Pallets! Inside there are cubes on pallets on shelves in aisles for miles!

(Not really miles.)

It is possible that some of these cubes might be actually storing things, but if so there's no obvious way to identify them. The robotic forklifts zipping down the aisles are certainly picking up or putting down particular pallets rather than the nearest available ones.

This place.

She'll come back out and take a left where the catwalk forked.

An unscenic walk past unportablable ridged yellow walls. The sound of machinery filling the air resolves into a — smashy — sound up ahead.

Here is a side branch leading to something that looks like a test chamber, standing out against the panel-arm-less rest of this area.

Here is a line of arms supporting panels with embedded Aperture Science High-Energy Pellet emitters, heading in the same general direction as the cubes were, but moving a lot slower.

As each one enters this processing station, the panel and outer shell is braced, and an arm with a tiny spiked panel on the end punches through the center of the device, ruining it. The arm retracts, clinging mangled bits are cleaned off, and the line advances.

What the... Okay this deserves some more careful investigation. Where are the pieces going? Where are they coming from?

Right, right. After some twists and turns and gratuitous rearrangements of how the emitters are being transported, she arrives at the emitter production line.

Here are lots of robot arms and conveyor belts and machines that do something-or-other to partially completed emitters. The least cryptic parts of the process are in the last two steps of the production line: first, shiny new panels arrive and are demounted from their supporting arms, have a hole lasered in their centers, and the emitter is mounted in the hole and joined to the arm. Then each one fires a High-Energy Pellet at a waiting catcher, presumably to test its proper operation.

There does seem to be something a bit off about the general behavior of the line, though. There are unnecessary movements — not just complications, but little back-and-forths. There are occasional missing inputs and everything has to wait. Despite all this, all of the produced emitters are passing the test.

The panels are arriving from the opposite of the direction she arrived from. She could try to follow them back, but there's no catwalk and she'd have to jump along a row of panels moving along a track — which, inconveniently, have their portalable faces facing down into the abyss. Alternatively, there are a couple of catwalks heading off to the left and the right. (How gridlike.) It's hard to tell over the noise of the emitter factory, but left seems to have more sounds of activity.

Is this a cue for her to turn around and leave? Maybe. But she knows she can deal with turrets—their bullets hurt but it'd take a lot of them to kill her—and active turrets might mean there's someone else there. She goes after the sounds.

Following the sounds leads to another factory section.

Here's an access door with a Material Emancipation Grid behind it. The sound of turrets firing at intervals is clear now.

As are some more unusual sounds, and voices. “Did I hit it? I hit it, didn't I?” “Uhhh, no bullets. Sorry."

...what.

Through the grid—if it was going to emancipate her ear canals it would've already—and exploring.