Cool codes and ciphers:
https://www.braingle.com/brainteasers/codes/
Awesome cryptography (fictional) book series:
https://helendennisbooks.com/books/secret-breakers/
The most interest cryptographic mystery (in my opinion): https://beinecke.library.yale.edu/collections/highlights/voynich-manuscript
Nuclear Cyber Security Challenge
Case File:
Code Book: