A rift has taken you to a barren, worn down facility. The walls are either a bright white, or are peeling off. Drawings and mantras written by what looks to be an insane person litter the walls. Looking up, you see a huge machine mounted to the roof of the facility.

GLaDOS: "Is that you? How did you escape from your...? No. You're not her. You're just another unwelcome visitor."

The machine retracts it's statement.

GLaDOS: "Welcome to the Aperture Science computer-aided Enrichment Centre. You must love science almost as much as me. Which is good news because I've almost finished rebuilding the test chambers after Wheatley's incompetence. I am a Genetic Lifeform and Disc Operating System. Your first test is to see how well you follow instructions. Feel free to use this glowing switch under me when you can be bothered to start."

A button opens up from the ground. You can press it to begin whatever this "test" is... Or you can try looking around the rest of the run down facility. Be careful though, GLaDOS sees wherever you go.