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Yoshino Kumano NP, Wakayama
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Waves carved Engetsu’s roughly 9-metre opening; around the spring and autumn equinoxes, the setting sun lines up with it. The “round-moon island” briefly frames the sun instead of the moon.
In 1733, poet Gion Nankai described its arch as a stone gate with one opening. The nickname 円月島 (“round-moon island”) came later: it appeared on a map around 1887 and was established by a 1908 hot-spring guide.
Coral cover at Engetsu’s underwater site fell from 36% in 2016 to 18% in 2017 after crown-of-thorns starfish, then to about 2% by 2024. A 2018 cold shock wiped out Acropora, but new juveniles appeared.
Engetsu is the last remnant of a once-longer chain of offshore islets, according to the Japan Tourism Agency: continued erosion wore the others away, leaving this solitary survivor.
Fragile pebble conglomerate has repeatedly collapsed at Engetsu since fiscal 2005. Shirahama Town filled cracks and protected the surface from the sea-facing side, keeping repair work out of the familiar shore-side view.
