This small Japanese town has the Guinness World Record for the deepest underwater post box.

When the postmaster of Sumami, Japan noticed the city needed a boost of tourism, he developed an interesting solution. He put a post box near the coast of the fishing town hoping that the novelty would attract divers from around the world and pique the curiosity of people everywhere.

Postmaster Toshihiko Matsumoto hoped that it would attract people to the Kii Peninsula, altering an old, red post box that had been in the town since 1999. He didn't know if anyone would care or if it would even work.

Over 45,000 pieces of mail later, it definitely seems to work.

The small fishing town sees thousands of travelers each year come into a local dive shop to purchase a water-proof postcard. They then dive down to the post box and drop off their notes. Kioaki Yamatani manages Sumami's dive shop, and he's the one responsible for diving down to the post box each day, collecting the notes, and sending them on to the post office.

The post box even caught the attention of Guinness World Records who determined that it was the deepest underwater postbox in the world at 10 meters (approx 32 feet).

Yamatani noticed that the seawater started to corrode the cast-iron post box, so they began rotating two boxes every six months. Each one gets a fresh coat of paint and a deep clean before being returned to the water.