Alright, I have two things:
1) Scaphism: An alleged ancient Persian method of execution. It entailed trapping the victim between two boats, feeding and covering them with milk and honey, and allowing them to fester and be devoured by insects and other vermin over time.
https://en.m.wikipedia.org/wiki/Scaphism
2) The Murder of Junko Furuta: Junko Furuta was a Japanese high school student who was abducted, raped, tortured and murdered in the late 1980s. Her murder case was called the "concrete-encased high school girl murder case", due to her body being discovered in a concrete drum. The abuse was mainly perpetrated by four teenage boys over a period of 40 days from November 1988 to January 1989.
Warning: This is EXTREMELY brutal once you get past the introduction. You might think you are tough, but it will scar you, and you will not forget it. If you take it as a challenge as I once did upon getting a similar warning, just know you'll spend the next 30 minutes reading and likely days thinking about it. If you'd rather not know, you won't be missing anything. Consider yourselves warned.