stand on the step, and half a second later it starts going up, with you on it. upon reaching the top of the next step (actually a tiny bit over) you step forward to the next step, but before you have the chance to do so a flat plate shoots out from under the top of the current step and places itself at your foot. As you step on it, the former step pulls itself under the new step ready to shoot out at the next step and continue. It works the same way downwards.
Falling down is avoided by an airbag that detects the falling person above the CS. But that's another idea for some other time.-- pashute, Nov 29 2019 [+]
The more expensive option perhaps would be to have lifting plates on all the steps that move up or down and allow the user to shuffle forward on the level. That gives me an idea...-- DenholmRicshaw, Nov 29 2019 random, halfbakery