A very long time ago I wrote a short story that was entitled "Outside." It was about a young woman who lives in an entirely enclosed city. She reads "myths" about a world outside the city walls, but does not believe the green earth and sky exist. She encounters a young man who claims to know they do, and eventually finds the exit to earth's old surface, which has been healing from many generations of abuse and pollution.
Like City of Ember and other dystopian fiction in which our world is a secret legend, Incarceron by Catherine Fisher has a similar theme. What I liked about this novel was the genuinely new way Fisher delivers her two worlds and the people inhabiting them. There's a strange feel of historical novels in the setting, mashed up with science fiction dystopia. I'm even getting soylent green moments, here!
I must say I'm really looking forward to the next installment, due out in December.