I've never used this in anger, but the following is a side-view of a protective zone I once built:
#################
#################
<- _ I _ >##
#### ####### #X##
##> _ I _ <##
##X# ####### ####
##< _ I _ >##
#### ####### #X##
##> _ I _ <##
##X# ####### ####
##< _ I _ >##
#### ####### #X##
##> _ I _ <##
##X# ####### ####
##< _ I _ <-
#### ####### ####
#### ####
#################
# = native rock
I = support, linked to pressure pads (not shown) and/or levers (wherever you want them...)
_ = bridges
>,X,< = stairway components
<- = indicators of ingress/egress, assuming it's to protect against enemies coming in from below.
And there's an option to make the open area below the support-suspended stack deeper and filled with the liquid of your choice. It could be used to kill (plenty of opportunity for "hammer and anvil" action) or incapacitate (from collateral cave-in effects). Depends on the creatures, and possibly how such things happen these days. As for re-setting, I think it would only partially work the same if rebuilt with constructed walls, but could still be an emergency airlock capable of even catching out flying enemies.
Alternatively, there's something very similar, that I've seen described, based upon a Support-supported stairwell stack in the middle of a shaft with only bridges connecting the various levels to the various shaft exits (Z+1 from the Support level has the lowest bridge to the lowest up-stairs). One emergency switch attached to the Support does... something.