My idea starts off with the character stepping off a train service of your choice, and onto the platform. A normal train journey, no expectations for anything out of the ordinary to happen whatsoever. But, as luck would have it, you fall through the platform you wanted to step onto. Not onto - into. Moments later, you find yourself thrown into a meeting with the head of some high school, who explains you are now in "The Gap," a space between dimensions. This particular part of the Gap is host to a twisted game, in which participants take a year of the school according their abilities, and must pass the end-of-year exams with at least an A. Otherwise, you spend a few thousand years being put through excruciating physical and mental torture, then you try again. Rinse and repeat as necessary. You can't die in the gap, but all other laws apply to humans - although death results in a week in what seems like a coma. And you can't afford to miss any classes here, unless you take option B, one seldom spoken of within earshot of a staff member. Option B is to escape from the school, brave the dngers outside, such as various monsters and traps which will maim you horrendously, and open the transportal. It's what was used to reel you in, and there's a chance it can be used to get you out again. Either wy, it's a gamble.