Since 2002, there is a postbox located underwater off the coast of a country. This postbox holds the Guinness World Record for being the deepest underwater postbox, sitting at a depth of 10 meters. It was established in 1999 to promote the country’s ancient Kumano Kodo pilgrimage trail and the surrounding areas in the southern part of Wakayama’s Kii Peninsula.
Around 1,000 to 1,500 pieces of mail are sent to this underwater postbox every year. An employee from the Yamatani Dive Shop collects the mail. To protect the postbox from corrosion caused by seawater, two iron boxes are used on alternate basis every six months. While one box is being cleaned and repainted, the other box is in use.
People can purchase water-resistant postcards from the dive shop and write messages on them using an oil-based paint marker. The items deposited in the postbox are delivered to their recipients within a week of being posted.