This is a type of ladder made from vines and planks or iron. It must be hung from the underside of a block.
Retractable Ladder Machine
The machine itself can be oriented any direction except facing up and down, and must be filled with rope ladders to operate. When supplied with a redstone signal, it will cause the ladder to unroll as far as it can (when it runs out of rope ladders or it can’t reach any further) and then retract.