I came across this "new" activity a few weeks ago and even though it was 40 ` out both boys were super excited to go on our first letterbox search yesterday. Actually letterboxing has been around since the 1800's but has become recently very popular with families. All you need is a rubber stamp, ink, notebook or journal, pen and if you look for the really cleverly hidden ones, a compass. We selected one from Atlasquest.com ( there are others like Letterboxing.org) to search for that seemed relatively easy, followed the clues and after a few wrong turns found the box and "stamped in".
Stamping in is the second step. When you find the box it will have a stamp and a notepad in it. You stamp your personal stamp in the box's notepad and write the date, your trail name (whatever you chose for these adventures), and where you are from. Then you stamp your notebook with the box's stamp and write any info you would like (it's your journal afterall).
The box must be replaced exactly where you found it so the next person to look for it can find it. Then you go online to Altasquest.com and post your find so the box's planter knows it is still safe and sound. My boys already have grand plans to do some urban box planting after only one find. Now that's a hit in my book.