Each day I place it in clear view of the boys, who are given the strictest instruction that they should NOT OPEN IT on any account. They can't wait for my back to be turned. What small boy could resist!
Inside, there's a small secret department into which I place a clue about hidden treasure. Nothing too complicated; they'll become more difficult in time. See Harvey J, above, holding one such clue.
Eventually they find two hidden gold coins (one each), filled with chocolate. They are always ecstatic; and I am too. Summer wouldn't be the same without Grumpy's book.
My apologies to George Eliot. I'm afraid I massacred a copy of her very first novel 'Adam Bede' in order to create my little game; but in the name of adventure, I think she might almost have approved.