Incarceron (Incarceron #1)

Finn has spent his entire life trapped within Incarceron, a colossal, sentient prison. He dreams of an 'Outside' that most prisoners believe is a myth, until he discovers a crystal key that connects him to Claudia, a girl living in the Warden's opulent world. As Finn plots his escape and Claudia faces an unwanted arranged marriage, they realize Incarceron holds secrets far more dangerous than they imagined. Their desperate bid for freedom will demand immense courage and come at a steep price.