Outlaw Cave - under the hood
There are two moving parts:
1. The stairs - each step moves individually between plates with slide. There is a one-plate-wide gap between the steps and the static part of the MOC to reduce friction.
2. The wooden floor downstairs - as you might see in the second part of the video, the black arm lifting the stairs is a bit too long not to collide with normal floor. Hence the floor has to 'wait' until the arm is lowered.
There are also some counterweights visible here, to make up for the stairs moving up. Thanks to them, it does not require much effort to lift the stairs up.
The mechanism works surprisingly smoothly.