An underground bunker is a fortified structure built below the ground level, designed to provide protection from various threats such as natural disasters, military attacks, or nuclear fallout. These bunkers can vary in size and complexity, ranging from simple shelters to elaborate facilities equipped with amenities for long-term survival. Typically constructed with reinforced materials, underground bunkers often include features like air filtration systems, water storage, and food supplies. They are used by governments, military organizations, and private individuals for safety and security during emergencies, reflecting a growing interest in preparedness and self-sufficiency in uncertain times.