Nestled into the Dodau Forest, about 250 kilometres (155 miles) north of Berlin, the Bridegroom’s Oak has a famous knothole that has been used as a mailbox since 1892. After an influx of letters in the 1920s, the tree received its own postal code.

Mail carriers from the German postal service deliver 50 to 60 letters to the knothole each month. They must climb a ladder to reach the arboreal mailbox about three metres (ten feet) up the 25-metre (82-foot) tall tree that’s more than 500 years old.

Visitors can read the letters, sent from all over the world and even respond.

“The resulting pen pal relationships have even led to a few marriages,” the postal service says, with up to 100 rumoured to have occurred.

Known as “Bräutigamseiche” in German, the Bridegroom’s Oak was first used as a waystation between a forester’s daughter and a chocolate manufacturer from Leipzig, according to the postal service. The forester initially opposed the courtship, so the couple left love letters for each other in the knothole.

They ultimately married, with the forester’s permission, under the oak’s leaves in 1892.

Now, anyone in the world can send their own love letter to: Bräutigamseiche, Dodauer Forst, 23701 Eutin, Germany.