Apparently we’ve never shared a Cryptex before! Made popular (and coined) by the Da Vinci Code, a Cryptex is a combination style lock originally used to store secret messages. You can make your very own using a few pieces of PVC pipe, some epoxy, and nuts and bolts!
Cryptexes have a clever design that cannot really be lock picked, without simply breaking it. In [Dan Brown's] novel, it was said that some Cryptexes stored a fragile vial of vinegar with the message written on papyrus — that way, if it was forcibly opened the vile would break, dissolving the thin papyrus note.
They work similar to a bicycle’s combination lock, where if the correct password is guessed, the tumblers inside align, allowing the two halves of the cylinder to come apart. It’s actually a very simple design on the inside, and the whole mechanism can easily be made by yourself with minimal tools.
Using PVC it’s a relatively easy project, although you could also make a much more impressive one out of metal instead, like this amazing one made from a copper pipe.