Setting the height is the key thing. That's what it comes back to. That's totally different from fiat-killing a PC like you suggested earlier. You have to set the height for your other suggestions to work too.View attachment 156272
EDIT: I'm going to exit the discussion here as clearly my intention is not getting across, but set the height to something that will likely kill all the players if they fall. That's it. I dunno what that is because the OP hasn't said the module, what level it's for, or much context at all really... but it's really just that simple. If you think that's unfair, set the height lower.
That's what was missing from the adventure, for literally no reason except laziness. It's not at all uncommon either in published adventures.