Treasure hunters are given an encrypted clue that leads them to their next clue.
A simple encryption is to replace each letter with the next letter of the alphabet (a becomes b, b becomes c and so on to z becomes a). This is a good encryption provided the hunters recognise what has been done. Alternatively a key could be given that maps out which letters have been swapped. The hunters could be given something like this (maybe with a previous clue?) to use to decrypt the clue: