I recall accidentally stumbling upon pictures of a trans women who cut off their own penis. I'm also aware of the murder and animal abuse videos by Luka Magnotta, and the execution videos by Al-Qaeda and ISIS. As well as various sites which feature cartoon porn depicting sadistic abuse or violence. (This could also include sites that are tolerant of this type of content even if they don't actually produce it, such as the so-called "incel" sites.
There's other stuff out there (e.x. incest porn) which is weird and gross, or individuals like Chris who advocate "consensual incest" or other fetishes (e.x coprophilia / scat fetish), but probably not as objectively offputting as stuff which is meant to depict violent or sadistic abuse. There are also weird sites out there dedicated to witchcraft, demonology, or the occult (possibly even including "spells" intended to kill or harm people) that I'm not sure where they'd fit into the "disturbing rankings". Or for that matter, websites dedicated to cult or cult-like groups (such as LessWrong, which is some kind of "transhumanist" or "AI" cult).
(Beyond that, I'm thankful to say I've never ventured onto the DarkNet with Tor and I never will, especially considering the amount of CP or other illegal content, such as hitmen or assassins for hire). Thankfully the most objectively disturbing stuff on the internet (such as the infamous child rape videos by Peter Scully or the child porn and child-sex trafficking rings on the DarkNet) probably aren't something anyone would ever encounter on the regular internet, unless they were perverts on the DarkNet who were specifically looking for it).
