As Chell travels deeper into the maintenance corridors of Aperture, GLaDOS makes increasingly desperate and unhinged pleas to stop that eventually turn into death threats. This culminates in her setting up multiple turret ambushes, each more elaborate than the last, to try and stop Chell. A rocket turret also gets in Chell's way, but she exploits its slow aiming and firing speed to make it destroy some windows blocking her path.
After making her way through the halls of Aperture for some time, Chell happens upon a slideshow presentation that reveals the company was created as a direct competitor to Black Mesa, only to fail miserably. It's just after this that she notices through some windows a conspicuously large chamber off in the distance...
