I am a little conflicted on what to say about this mystery. It certainly is well thought out and nicely done!! I received the whole package at once so we could do it over the week the grandkids, who are 8 and 5, were with us. The 8 year old was just too smart in that, right from the first letter, she didn’t think it was real - that it was somehow some sort of scam. How would they know who we are and where we are, et cetera? Also, that first letter really wouldn’t have been enough to carry their interest for another week, so we did the second one several hours later.
Because we didn’t have access to mail where we were, I just slyly put each installment on the door mat outside the front door and we set a timer on the phone that sounded like a doorbell so they’d think someone dropped it off. They were always very excited when the “doorbell" rang! Accompanying the various letters were fun and interesting things such as keys, maps, and ciphers. There sure was lots of excited jumping up and down and wild screaming when the last installment was a package!
The whole Treasure Hunt mystery was very cute and impressively done. That said, I’m not sure the 8 year old would look forward to doing another - though we probably will try another one again next year.
P.S. Hint: you might want to have a keychain of some sort handy for your kids so the tiny keys don't get lost.