Okinoshima is a remote island in the Genkai Sea, roughly 60 km off the coast of Munakata City, in Fukuoka Prefecture. The people of the Munakata region call Okinoshima “kami yadoru shima,” meaning “sacred island” (or literally, “island where god dwells”). For a period of roughly 500 years, from around the latter half of the fourth century, large-scale religious rituals were conducted on the island. It has been carefully protected to this day as an object of worship; a sacred island that people are not readily allowed to approach. It is because of this that untouched primeval forests and the remnants of ancient ritual sites remain on the island to this day.

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Long before the shrine was built, Okinoshima was used for rituals involving prayers for oceangoing ships and trade ties with Korean and Chinese people, the Japan Times reports.

Thousands of artefacts brought as gifts from overseas have been found on the island, including gold rings from the Korean Peninsula, it says.

Okinoshima male visitors are welcomed on 27 May only

While the reason that women are banned is unclear, some believe that it is because menstruation would defile the site. Others say that women were banned from travelling because the journey by sea was considered dangerous, and men wanted to protect child-bearers.

The island now welcomes visitors on a single day every year, 27 May, and ancient rules are still observed.

The number of visitors is restricted to 200. They must perform ablution rites in the sea, and – most controversially – be male. When they leave they are not allowed to take away any souvenirs, or disclose details of their visit.