Yonaguni

24.4333°N, 122.9333°E.

Submarine rock formation off the south coast of Yonaguni Island, the westernmost inhabited point of Japan. Discovered in 1986 by diver Kihachiro Aratake. The principal feature is a stepped sandstone formation approximately 50 metres long and 20 metres tall lying in 25 metres of water; surfaces include sharp 90° angles, rectilinear terraces, and what appear to be staircases, channels, and a turtle-shaped relief. Marine geologists Robert Schoch and Masaaki Kimura disagree publicly about its origin: Schoch interprets the structure as natural sandstone fracturing along bedding planes; Kimura argues for human modification of natural bedrock during the late Pleistocene, when the area was above sea level. The site sits on a region last submerged approximately 10,000 BCE.

A submarine staircase 25 metres down is either Asia's oldest building or a coincidence with right angles — the geologists who have actually dived it cannot agree.