I want to add a couple of good ones I’ve found:
Jeff the Killer lost media: no one knows where the original Jeff The Killer image came from.
Mortis.com: old weird website
Also here’s a good website on various obscure computer/Internet related oddities: https://suricrasia.online/iceberg/
Honestly this one is for our benefit, A lot of stuff thats free and universally compatable (like email) is that way because the ancient sages who forged the internet built the protocols for that shit into its very backbone so no one could fuck it up later (wether by incredible forsight or lazy implementation who knows). The day someone at google re-discovers/deciphers how all that shit works at once is the day a lot of stuff we don’t even think about suddenly turns into walled gardens.
To be clear despite some dramatic word choice its not like lost knowledge or anything but its obscure enough that no single person likely has all the pieces to safely make any signfiicant changes.