An Underground City refers to a network of subterranean spaces that can include shops, homes, and public facilities. These cities are often built beneath existing urban areas to maximize space and provide shelter from harsh weather or natural disasters. They can be found in various parts of the world, with notable examples like Montreal's RESO and Wellington's Underground City. These underground environments are designed to accommodate large populations and facilitate movement between different areas without the need for above-ground travel. They often feature amenities such as transportation systems, restaurants, and art installations, creating a unique urban experience below the surface.