This geomorph is perhaps not as exciting as the others, since instead of a statue or portcullis, it features a simple but underused feature: barred doors. You'd think that more published modules would use these, but they seem pretty rare, in my experience.
Anyone retreating to the central room on this geomorph can bar both entrances, then descend two levels to an escape tunnel that runs below a room that exits to the left of the geomorph. The GM can make it easy and include a ladder in the escape tunnel that climbs one level to the exit, or the PCs can be stuck trying to figure out a way to the trap door in the ceiling. If the doors are barred and the secret doors remain secret, the PCs can't pass from the right side to the left side of the geomorph.