Underground engineering is an interdisciplinary research field and methodological approach concerned with the planning, design, construction, and operational challenges inherent in situating complex facilities beneath the Earth's surface. It investigates the geotechnical, structural, and environmental interactions specific to subsurface environments, integrating considerations such as geological stability, hydrostatic pressure, and specialized requirements like passive shielding or containment for sensitive applications such as nuclear facilities. Its significance lies in enabling secure, stable, and isolated environments critical for specific scientific research or industrial processes.