The provided sources detail the reality series Expedition Unknown and its investigation into the Yonaguni Monument, a massive underwater rock formation off Japan featuring symmetrical, pyramid-like steps.This site is the focus of a long-standing scientific debate between researchers who believe it is a 10,000-year-old man-made city and geologists who argue it is a natural product of tectonic stress and erosion.While some researchers point to potential tool marks and stone artifacts found at the site as evidence of human construction, the true origin of "Japan’s Atlantis" remains one of the world’s great unsolved mysteries