Susami, a small fishing town on the Kii Peninsula in Japan's Wakayama Prefecture, struggled towards the end of the 1990s to offer tourists a reason to stay rather than just pass by on their route to somewhere larger. With only a few thousand residents and no notable landmark to divert tourists from the major coastal route, local authorities were searching for anything unique enough to place the town on a map that largely disregarded it. The man in charge of the neighbourhood post office gave a somewhat surprising answer. As part of a local fair intended to promote the neighbouring Kumano Kodo pilgrimage trail, Toshihiko Matsumoto, who had worked for Japan's postal office for around forty years, suggested erecting a functional mailbox on the floor of Susami Bay. The community dropped a red postbox to a depth of around ten metres, or thirty-three feet, in 1999 with the assistance of a local dive shop, and connected it to the postal system as an officially recognised collecting site.
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How the underwater postbox works
Divers first buy a waterproof postcard and write their message on dry land with an oil-based paint marker before entering the water. They carry the completed card down to the postbox and place it inside the cast-iron box, which is designed to keep the mail from drifting away while remaining open to the surrounding water.
The town rotates two boxes since the metal box rusts steadily in seawater. Every few months, the one in use is replaced so the other may be repaired and painted before it collapses again. Nearly every day, a dive shop employee goes down to the box, picks up whatever has gathered, and, just like any other piece of mail, carries the postcards to the Susami post office for the last leg of their journey. Record keepers were persuaded to take the underwater box seriously in part because it actually feeds into the regular postal network rather than existing only as a curiosity.
Earning a place in the record books
By the early 2000s, word of the unusual mailbox had spread widely enough among divers that the site was formally recognised by Guinness World Records as the deepest underwater postbox in the world, a title which said that in the first year of the box's life, almost four thousand pieces of undersea mail had been collected. The record helped transform a small fishing hamlet into an unusual stop for scuba divers who go to the Kii Peninsula just to mail a postcard from the ocean below.
Divers who make the trip often describe the experience as oddly touching, less because of the postcard itself than because of the weird thrill of seeing an utterly quotidian act of communication take place in a place where it was obviously never meant to be. Almost two decades after Matsumoto initially proposed the idea, the numbers interested in the project had risen well beyond what anyone at that original fair could have expected.
Twenty years of mail under the sea
A documentary produced in 2018 recorded that nearly thirty-eight thousand waterproof postcards had been mailed from the Susami postbox since it first went into the water, a milestone achieved almost solely through word of mouth among divers rather than any continuous advertising push. Matsumoto didn't live to see the project become so famous, but the dive shop owners who inherited the care of the box still talk about the idea as the one thing that made Susami so well known. What started as a rather modest gesture, a postmaster’s idea of livening up a local fair, has outlived the fair itself by more than two decades, proof that sometimes the tiniest ideas at a town festival are the ones that go the farthest.
