Yonaguni Monument

The Monument is a mass of layered sandstone the size of a building, cut into flat terraces, straight edges, and stark right angles, found in 1986 by local diver Kihachiro Aratake while scouting hammerhead grounds. Whether people shaped it is a genuine, unresolved argument. Marine geologist Masaaki Kimura spent years cataloguing what he interpreted as tool marks, drainage channels, and even carvings; most geologists respond that this sandstone naturally fractures along horizontal bedding and vertical joints, producing staircase forms without any hands involved, and that similar geometry appears on the island's shoreline. Diving it, you sweep across the main terrace, duck the surge behind the prow-like corner, and understand why both camps sound so sure of themselves.

Il momento che aspettavi: The terraces and right angles themselves, the natural-versus-carved debate, big Kuroshio visibility

Topografia: Massive stepped sandstone formation rising from about 26 m toward the surface

Corrente: Kuroshio-driven flow and surge over the terraces are routine; calm days are the exception to plan for.

Entrata: Short boat runs from the island's harbors; entries are timed around surge and the current wrapping the south coast.

Pericoli: Surge over the terraces, current at the corners, and swell surface intervals; listen hard to the local briefing.

Nitrox: Vale la pena qui — i profili rientrano nella fascia in cui l'aria arricchita (nitrox) prolunga in modo significativo il tempo senza decompressione (con la formazione necessaria per utilizzarla).