This sort of thing has been going on for over a hundred years on Dartmoor. They call it "Letter Boxing" here. They leave an ice cream comtainer or similar box, sometimes an old ammunition box, in a spot on the moor. This box contains a book and a rubber stamp put there by the person who puts the box out. They then give out a grid refference with some clues of how to find it. The people who go looking for them also carry a stamp and a book or cards. They stamp the book in the box with their stamp and stamp their book with the stamp in the box.
They do have one rule in their code of practice that states that no box should be put on any ancient monument. They seem to stick to it as I have never found any at any of the sites I have visited. I have seen some nearby though .
The problem with it however is it causes so much errosion around the area where the boxes are put, from people walking around looking, that they are very easy to find. If I spot any while out walking I always move them to another spot nearby to help the area recover and give them a bit more of a challenge.
Peace , Lubin
