LEMMiNO has a nice 18 minutes documentary and summary on Cicada 3301: https://www.youtube.com/watch?v=I2O7blSSzpI
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Some "internet lore" off the top of my head:
* Body builders try to figure out how many days are in a week, summary dramatised here: https://www.youtube.com/watch?v=eECjjLNAOd4
* Time Cube: https://timecube.2enp.com/
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EDIT: speaking of SilvaGunner, I've never heard this name before, I found two mentions of it on two unrelated YouTube videos in the past 3 hours. Incredible. Baader–Meinhof strikes again.