Is there a underground world

The concept of an underground world often appears in mythology, literature, and various speculative theories, but there is no scientific evidence to support the existence of a hidden civilization beneath the Earth's surface. While there are extensive cave systems and subterranean ecosystems, they do not constitute a separate world in the fantastical sense. Some fringe theories suggest the possibility of advanced civilizations living underground, but these remain unverified and largely fictional. In summary, while intriguing, the idea of an underground world lacks empirical support.