The Demon Challenge is a Portal 2 test chamber I saw in a dream like an hour ago and had to write down. It could appear without prompting, on the workshop, or in real world transit systems. I do not know why it is called The Demon Challenge: this name appeared just after I had woken up and just before I began writing this down, not in the dream itself.
THE OBVIOUS SOLUTION: The Demon Challenge appears to just be a single-line train station, with a subway train ready to leave. Attempting to travel down the stairs to reach said train results in the stairs shifting erratically and soon being individually closed off with barriers, meaning it is completely impossible to reach the crowded subway train.
THE REAL SOLUTION: One must then pay attention to the testing elements in the chamber. A portal device is needed to solve The Demon Challenge. The solution is relatively simple once you realize you need to do it. One must use a portal to cover the ramp next to the stairs with propulsion gel, then run along the ramp to cross the subway line and reach the other side. There is a chamber lock there, which will open to let you out. At which point you will find a second gray chamber lock clipped into the real chamber lock, making it impossible to leave.
