The Dark Hills Divide by Patrick Carman
Elyon is a land of dark hills, enchanted forests, and great walls that connect and encircle the cities of Lathbury, Turlock, Lunenburg, and Bridewell like spokes in a wagon wheel. On her annual summer trips to Bridewell with her father, the mayor of Lathbury, Alexa Daley spends much of her time dreaming of escape. Having lived within the walls all of her 12 years, she wants nothing more than to explore the uncharted wilderness beyond. But, the walls are heavily guarded, and frightening legends suggest that forests and hills are no place for a child–especially a young girl. When a mysterious conversation and an unfortunate accident put Alexa within reach of a way outside the wall, she must decide–heed the warnings of her elders, or satisfy her curiosity and unravel the mysteries of Elyon.