Crowbcat created a Portal setup that had Chell, the game's heroine, trapped between two portals that crushed her. The results were an astounding wonderland of psychedelic visuals
I don't know what would be cooler: if this were an emergent property of the game's programming, or if the designers hid it in the code and waited for an adventurous sort to discover it.
Everything has been recorded at first-person perspective. It resulted in infinite psychedelic visuals such as giant spirals, never-ending walls, and gigantic perpetual portal rooms. Scary at first when you realize you're face to face with yourself. Such visuals potentially can trigger anxiety about mirrors and stairs to some people. There is no way to get out without restarting or using cvars. Chell doesn't die by doing this, and it looks like there's no gravity anymore.
Crushed between two portals experiment