If you got nothing to do for the weekend and have a couple extra YEARS to spend trying to solve a problem here is a great place to start. It is a list of many of the worlds most famous unsolved codes, ciphers, and languages. Solving any one of these will bring you fame and fortune (as I guarantee you will be able to find a security job somewhere!)
…and just a quick word of advice, don’t bother trying to solve the Voynich Cypher.