Around age 15, I started the story that I'm still continuing today. It is hilariously geeky but grows progressively darker; I actually set it up so that it could.
The story starts with a street prostitute (Janelle, a name chosen because I don't know anyone with that name; her image in my mind is tailored to not look like anyone I know) entering the doors of a skyscraper. This place is the biggest, strangest brothel on Earth, and the higher up you go the worse it gets. The ground floor is just a strip club, and a pretty cheerful and chummy one at that. Girls dance around in bikinis and chat with the boys, there's not even a Champagne Room, it's all in good sweet fun. On the second floor the girls will get a little nakeder, and the clientele is a little rougher. Few floors above that, they'll fuck you, or have sex on stage. Few floors above that, they'll do it up the butt or let you spank them a bit.
Around the thirtieth floor, girls are being locked in boxes with a hole in the back so they can't see who's fucking them and they can't stop it. Around the fortieth, electrodes are being used so the pain will make the girl involuntarily squeeze her muscles around the guy who's fucking her at the time. Around the fiftieth, there are dildos that make forearms look like foreplay, and no, you're not expected to take them consensually.
The men are always very anonymous and generic in my mind. The women being violated get all the focus.
I never numbered out exactly how many floors there are and exactly what happens on each one. Sheesh, that just would be weird. But I did have one thing figured out from the start. The top floor is said to be unspeakable.
Janelle was, of course, a trooper. Over the course of my late adolescence, in ten to forty minute installments, she made her way up the tower. I was 18, I think, when she reached the top floor.