I forgot to add a lnike here it is https://uboachan.net/mado/
You can find a lot of old boards like that one at https://uboachan.net/annex.php
. There are some actual hidden boards but whenever you remember one a child vomits, best not to think about it.
Those are all old and archived boards that are no longer active. At least someone cares enough to remember them.
Good for you I guess…