Sometimes, it's what outside of a level that's really interesting.
If you haven't come across Boundary Break on YouTube before, it's basically a channel that uses console commands, cheats and whatever trickery is necessary to explore the environments outside the confines developers put on players. Developers often hide textures, additional room, easter eggs and other bits and pieces outside the player's view, and unlocking the camera and clipping through walls is often the only way to find them.
The latest journey takes us through the walls of Portal 2. It's intriguing how dark some of the levels are once fog is turned off, and what Valve did with some of the textures placed out of bounds. Or companion cubes.
Also, when Chell hits the stalemate button at the end of the game? Her character model turns into a pair of arms:
You can view the full Boundary Break video below, and the full playlist here.