A letterbox is another form of treasure hunting using clues instead of coordinates. Once a letterbox is found instead of signing a log book, you place your stamp mark in the letterbox's log book and place the letterbox's stamp into your own log book.
In some cases such as this, a letterbox hybrid has coordinates, making it a letterbox and a geocache. You can leave your stamp and get the cache's stamp in your own log book as in letterboxing, or you can simply sign the log book as in geocaching, or both.
This letterbox hybrid contains: - A log book. BRING YOUR OWN PEN AND INKPAD. - A rubber stamp is there. PLEASE LEAVE THEM IN THE CACHE!!