National Underground America Day is observed on May 14th and honors the approximately 6,000 North Americans who live in underground homes. This day celebrates the unique architectural innovation of subterranean living, which offers benefits such as natural insulation, energy efficiency, and a seamless blend with the environment. Founded by architect Malcolm Wells, the day encourages exploration of underground spaces and promotes sustainability. Typical customs include visiting local caves or underground tunnels, hosting themed parties, screening films set below the surface, planting root vegetables, and building blanket forts. The celebration highlights the potential of underground living to foster a deeper connection with nature and promote energy conservation.