In the Dodau Forest in Germany, a 500-year-old oak tree has been connecting people from all over the world in a simple, yet special way. Since 1927, the tree has had its own zip code. Five to six letters arrive each day, written by people searching for true love, life advice or even just a penpal. Visitors of all ages come to the tree, climb up a wooden ladder and fumble for the letters stored in the tree's knothole.
Karl Heinz Martens has been delivering letters to the oak tree for more than 20 years. Now retired, he reflects on its popularity and the nostalgia people feel reading handwritten letters from strangers in a forest environment that feels much calmer than the outside world.