
He placed an invisible link on his website. Only visible by reading the page content (html). Then the bots followed the link. This link lead to a page with 5 links (door) four links are dead and one leads to another page (level) with again 5 links.
I guess the links and pages are generated on the go. So the bots and crawlers may follow the links forever of they like.









As some other users have already mentioned it, have a look at this project anyway: https://iocaine.madhouse-project.org/
It gives much more bloated information for a crawler than I expected. But sounds quite fun to host.