On this site you can try solving cryptographic challenges.
The difficulty ranges from pen & paper type riddles and ciphers to modern encryption algorithms and even yet unsolved problems.

So if you're bored and like solving riddles or ciphers this might be a nice challenge.

https://www.mysterytwisterc3.org

Coool

Hahaha lol

neat

(i dont wanna accidentally bump this off the page, so up)

Thanks Kafka!

nice :D