Going even further than Pasolini's version that is already impossible to watch without turning your eyes away at some point, a ten-hour version of the 120 Days of Sodom, putting in motion even the parts left unfinished by Sade, would be unforgettable. In particular the very last torture. The text is available on Wikimedia. I dare you.
As a avid reader, I also think of an adaptation of Histoire de l'Oeil (Story of the Eye) by Georges Bataille, in fact, of any work Bataille made (it's sad he's only remembered for his erotic-psychanalytic works and not for his beautiful philosophical reflections on fascism). Story of the Eye is quite short, and there is a moment, in a church, where an eye is put in a woman's...Well, you see.