The 17-minute video describes the bizarre Cicada 3301 mystery

I've heard bits and pieces about Cicada 3301, which is rumored to be an elaborate alternate realty game, an anonymous pro-privacy collective's search for new members, or an unknown intelligence agency's stealth recruiting program.

Whoever set it up spent a lot of time, money, and thought into creating the online and physical clues designed to challenge fanciers of cryptography and computer security.

This video does a nice job explaining Cicada 3301 from its first post on 4chan in 2012 up until 2018 (when the video was posted).