I remember in the 2000s, there was some site using a decimal IP address (as a single number, not dotted quad) that had hacking/crypto puzzles. Something with a "Alice in Wonderland" theme. Does that ring a bell for anyone?
Was it called ninebows? I was looking online for that a while ago to show a friend, and I remember in school reading pages and pages of forum threads about it: speculation of what this or that meant, ideas for solving the next puzzle, et c. It was a website with some hidden puzzle that, once solved, would leave you with another link somewhere else with another puzzle that needed solving.
Someone eventually won, too, but it looks like it just vanished off the face of the Internet like many things from that era. Either that, or my search engine skills aren't good enough.