The word "impregnable" is employed across literary works to evoke images of unassailable strength, whether referring to physical fortresses or the steadfastness of character and ideas. In historical and adventure narratives, it often designates a stronghold virtually impossible to penetrate—for instance, a city or rampart described as impregnable [1] or majestic fortifications crafted to resist any assault [2, 3]. In a more abstract sense, the term extends to personal resolve and moral fibre, illustrating an inner domain or virtue that remains untouched by external threats [4, 5, 6]. At times, it even frames societal or institutional constructs as impervious to change or criticism [7, 8], thereby reinforcing its power as both a literal and metaphorical marker of ultimate defense.