We use cupped hands for the kid to step on.
and she's stuck there until morning. Well she can get down on her own if need be, just not back up.
While a ladder would be cool, I'm just not sure how it wouldn't be in the way. It if sits flat against the beds, then no one can get into the bottom bunk. If it angles out, it's in the way of the bathroom door being fully open and the walking area.