Cardboard inside BB shell

A friend of mine told me that his daughter had found a hole in the ground on Primrose Hill - with a little wooden lid on the top - it's very hidden and very very hard to find - inside the hole (around a couple of feet deep) was a tube, and inside that tube was a smaller box - and inside that box was a small book and a pencil.

As I live around the corner from the hill he gave me directions, it's really hard to find, if I remember right it's so many steps from a certain tree going North, then so many steps towards another tree and so on . . .

Anyhow, one night, I managed to find it, it was very very strange, the book was full of the names of people who had found the box, a few business cards and a few weird trinkets, I put my name in the book and stuck it all back.

I had almost forgot about it completely until your post reminded me.

http://en.wikipedia.org/wiki/Letterboxing