As global urbanization accelerates and surface land becomes increasingly scarce, cities worldwide are turning their attention to the untapped potential of subterranean space. This paper examines the emerging trend of underground megaprojects as a transformative solution to contemporary urban challenges. Through comprehensive analysis of current developments, technological innovations, and case studies from major metropolitan areas, this research demonstrates how subterranean infrastructure projects are reshaping urban planning paradigms. The study reveals that underground megaprojects offer significant advantages including efficient land use, environmental sustainability, disaster resilience, and economic optimization. However, implementation faces challenges related to initial costs, technical complexity, regulatory frameworks, and social acceptance. The findings suggest that strategic integration of underground space development is essential for sustainable urban growth in the 21st century, requiring collaborative approaches between planners, engineers, policymakers, and communities to realize the full potential of this underground renaissance.