"Underground" refers to spaces or activities that occur below the surface of the earth. This can include tunnels, subways, or even hidden communities. Many cities, like New York or London, have extensive underground systems that help people travel quickly and efficiently. These areas can also be home to unique ecosystems and wildlife, showcasing a different side of nature. In a cultural context, "underground" often describes art, music, or movements that exist outside mainstream recognition. For example, underground music scenes feature independent artists who create innovative sounds without commercial pressure. This underground culture fosters creativity and allows for diverse expressions that challenge societal norms.