I've been looking for years for a board that I found by complete accident a long time ago, and I'm sure someone here must have visited it as well.
All that I remember is that the link to it used to be buried deep inside 7chan's source, but I don't think it is anymore, and that the song "Moskau" by "Dschinghis Khan" played constantly in a loop. I think that song was played on the page that would go up whenever 4chan was down to drive away flooders too, which was the way most people found about it.
This short response thread is the only clear reference to it I've been able to find, which at least proves I'm not misremembering things:
https://desuarchive.org/gif/thread/12877469/#12887923