Minecraft wiki entry for Ladder, associated text: Opened ceiling on water.
Tunnel through water.
Ceiling lit by ladder-suspended lava.
Naturally occurring ladders in a stronghold.
An mineshaft has intersected with a stronghold resulting in floating ladders.
In versions prior to Beta 1.5, spacing ladders was a way to climb, without wasting ladders.
No air-pocket is made in Java Edition 1.13.