I'm aware that it's old, but I only recently decided to read it. This was an excellent decision. I'd guess that it's about an hour's worth of content, but what an excellent hour it is. I don't want to spoil anything, but it may not be for the faint of heart.
Ruby Quest is a choose-your-own-adventure mystery story that was hosted quite a while ago. It features Ruby, a bunny girl who wakes up one day in a "cell/locker/coffin" with no knowledge of how she got there. The readers' role was to provide commands that would eventually lead to her escape. As it has been finished for quite a while now, there is no longer any way to influence the story, so it reads kind of like a webcomic. If you have experience with Problem Sleuth, it's like that. I really, really don't know what else to say without spoiling stuff, but it's definitely worth a shot.
If anyone needs a version that doesn't rely on Flash, let me know. I link people to this one because of the two I looked at, it's not missing any panels, but I will legitimately reread all of Ruby Quest to double check for a proper host if needed.