Incarceron

Incarceron is a prison so vast that it contains not only cells, but also metal forests, dilapidated cities, and vast wilderness. Finn, a 17-year-old prisoner, has no memory of his childhood and is sure that he came from Outside Incarceron. And then Finn finds a crystal key that allows him to communicate with a girl who claims to live on the Outside.
Incarceron is a prison so vast that it contains not only cells and corridors, but metal forests, dilapidated cities, and wilderness. It has been sealed for centuries, and only one man has ever escaped. Finn has always been a prisoner here. Although he has no memory of his childhood, he is sure he came from Outside. His link to the Outside, his chance to break free, is Claudia, the warden's daughter, herself determined to escape an arranged marriage. They are up against impossible odds, but one thing looms above all: Incarceron itself is alive . . .