One Time Pad
A one time pad is virtually unbreakable, when used correctly. This cache shows an example of one time pad cipher that can be broken as the encryption mechanism is described and how the key is derived. It is just a matter of simple programming.
Mastermind: Traingle Edition
We all played Mastermind, the board game. Now, you can also play it to find a geocache. Have fun guessing the answer and using the clues provided to find the correct coordinates where the caches is hidden.