Scuba posting An underwater mailbox (すさみ海中郵便ポスト Susami Kaichu Yubin-Posto) can be found at a depth of 10 meters off the coast of Susami, Wakayama, and is certified as the "World's deepest mailbox" in the Guinness Book of World Records 2002. Special plastic postcards (�150 domestic, �350 international) are available, and divers mail nearly 200 items daily in the summer peak season. The mailbox is open from April to September. |