The City of Ember (Jeanne DuPrau)

Summary: The city of Ember was built as a large refuge for the human race. Two hundred years later, the great lamps that light the city are beginning to dim.  When Lina finds part of an ancient message, she's sure it holds a secret that will save the city.  Now, she and her friend Doon must race to figure out the clues to keep the lights on.  If they succeed, they will have to convince everyone to follow them into danger.  But if they fail?  The lights will burn out and the darkness will close in forever.  (from amazon.com)

Where can I find it?: Lower/Middle library, Lithgow building AND Upper School library, Walczak building

Tags: Occupations; Fantasy fiction; Messengers; Imaginary places; Civilization, Subterranean; Escapes; Underground areas; Electric power