The City of Ember Book 1 by Jeanne DuPrau

The provided text excerpts introduce the dystopian city of Ember, a seemingly isolated underground civilization built by "the Builders" who left behind secret instructions for "Egress," or the way out, entrusted to the city's mayors. The story follows two twelve-year-old protagonists, Lina Mayfleet, a messenger, and Doon Harrow, a Pipeworks laborer, who are keenly aware of Ember's worsening state, marked by frequent blackouts and dwindling resources. Both children are searching for a solution to save the city; Lina discovers the damaged instructions left by the first mayor, while Doon investigates the failing generator and the Pipeworks tunnels, where he uncovers the current mayor's secret stockpile of stolen goods. Eventually, the two decipher the instructions, which describe a river journey via boat, leading them through a hidden passage to the surface world and the journal of one of the original Builders, confirming that Ember was a time capsule to preserve humanity after a catastrophe.