The corridor up ahead is the extremely age-worn version of the chamber where she got the blue portal gun for the first time. One of the walls has holes though and Wheatley is there. "H-hey! You made it!"

"Yep."

Is there perchance a blue portal gun in the place where the blue portal gun goes?

"There should be a portal device on that podium over there!" Wheatley calls, coincidentally enough. "I can't see it though... Maybe it fell off. Do you wanna go and have a quick look?"

It seems to indeed not be there.

She goes and looks. And opens her ground, in case it's out of sight but still around here somewhere. She remembers very well what those things feel like.

No portal device but the ground is rather hollow beneath her feet and "Whoa!" he exclaims when it crumbles into an extremely deep hole.

—clearly she should've been paying attention sooner. She gets up and dusts herself off.

"Hello? Can you see the portal gun?—also are you alive, that's important, should've asked that first..."

"I'm alive! Still looking for the portal gun."

"Brilliant! I'll wait for you up ahead then!"

"...'kay."

The space around her is a rather dank tunnel, possibly some particularly derelict chamber. There's light coming from up ahead though.

She goes thataway, keeping alert for unstable footing and any sign of a portal widget.

There's a bunch of debris over there and something that looks a lot like an orange portal on that wall...

...and yep, a portal gun on top of the debris.

She picks her way carefully over to the pile, retrieves the device, and makes a portal to get up to the orange one with. It feels very satisfying.

There are stairs! In ridiculous disrepair! That lead to a room with the computers she saw once. They're all offline.

Huh.

Farther along the corridor there is a broken window leading into what's probably yet another test chamber.

"Some emergency testing may require prolonged interaction with lethal military androids," says the announcer voice once she reaches that place. "Rest assured that all lethal military androids have been taught to read, and provided with one copy of the Laws of Robotics. To share."

The chamber itself is the deteriorated version of another chamber she's already been through, with a shallow pit separating her from the orange end of the portal and, presumably, the door out on the other side of a second shallow pit.

Wow this place is trashed. Boopty boopty boop, off she goes.

"Good! If you feel a lethal military android has not respected your rights as detailed in the laws of robotics, please note it on your self-reporting form. A future Aperture Science Entitlement Associate will initiate the appropriate grievance filing paperwork."

Emancipation grid!

Abruptly and mysteriously nonfunctional emancipation grid! Onward!

"This next test is very dangerous. To help you remain tranquil in the face of almost certain death, smooth Jazz will be deployed in three, two, one..."

Smooth jazz starts playing as she steps into another decrepit version of an old chamber.

It's so decrepit. Gosh.

Blah, blah, cube, button, she idly wonders if she can figure out how to break the door so it opens without her having to solve a puzzle first but the puzzle is so easy she doesn't bother trying.

The jazz cuts off before she has a chance to even get to the cube.

The next chamber is directly on the other side of an Emancipation Grid, and is yet another familiar one, with two floor-level buttons connected to the door, two raised platforms (one of which has a portal and the other a cube), and a pit where a second cube is.

This is boring. Boopty boopty boo, cube cube button button.

"Great work! Because this message is prerecorded, any observations related to your performance are speculation on our part. Please disregard any undeserved compliments."

On the other side of the door there is a room with a low glass ceiling above which a higher ceiling has an orange portal.