Discovered in 1986, the underwater Yonaguni Monument is a massive stepped structure with terraces, sharp angles, and towering walls that resemble a submerged pyramid or ancient plaza. Divers report geometric formations such as straight corridors, platforms, and a vast “staircase” descending into the seafloor—features that some believe indicate a lost civilisation, while geologists argue they may be natural sandstone fracturing. Strong currents and sudden pressure shifts in the area have led to stories of strange shadows moving across the monolith and unexplained lights flickering in the deep.