Underground facilities are structures built below the earth's surface, designed for various purposes such as storage, transportation, or habitation. These facilities can include subways, mines, and bunkers, providing essential services while minimizing land use above ground. They are often constructed to protect against natural disasters or military threats. The construction of underground facilities involves careful planning and engineering to ensure safety and stability. Factors like soil type, water table levels, and seismic activity are considered during the design process. These facilities can also help reduce urban congestion and provide efficient transportation options, contributing to sustainable development in cities.