unconquerable

This term conveys a sense of absolute permanence and resilience, suggesting a barrier or a spirit that cannot be broken regardless of the force applied. It carries a high degree of intensity, often evoking a feeling of awe or frustration depending on whether the subject is an ally or an enemy.

When applied to physical structures, it implies an impenetrable defense. When applied to human psychology, it describes a level of determination that transcends ordinary persistence, bordering on the supernatural or the heroic.