It is our secret hiding place, where we leave things and stuff for each other.
At first we looked for a hollow in a tree, but most were already in use, crammed with other peoples' secrets.
So we decided to exchange our secrets in plain sight, in a letter box.
Mostly we leave letters for each other, sometimes written in code or using symbols, just to build an air of mystery for prying eyes, but usually stating nothing more than our love for each other.
When we are unable to write, we leave snippets of conversations. Words mingled with lilting voices and whispers.
Occasionally we leave songs, or poetry, or an oft repeated refrain, or other plays of words and music and melodies.
Sometimes we leave each other our thoughts, and that is how we find we can read each others' minds.
Sometimes he leaves me a rose, and I am enveloped in its fragrance all day.
I leave him a feather and his imagination takes flight.
That's how it works each time.
One from him, one from me.
Once he left me a life, and I used it to cheat Death.
I have yet to figure out what to give him in turn.