CIty Of Ember by Jeanne DuPrau

City of Ember a beautifully wrote young adult, science fiction, fantasy type novel,about an amazing adventure that three minors Lina, Doon and Poppy embark on in search for the light outside the City of Ember.
The City of Ember was built centuries ago to protect the last of the human race from extinction. The city was suppose to be sustained throughout only 220 year and the box of instruction was left from the two builders on how to escape from the city if situations get bleak. The box was passed down over generations of the mayors but when it reached to the seventh mayor, the box was lost and forgotten about. 241 years have past and people are running wild with low supple of food and light.