The Land of Elyon BOOK 1 "Dark hills divide"

This book is about a girl named Alexa Daley. Her 3 cities are protected by enormous walls. Everyday she wonders wether the walls are to keep us in or to keep something out for it is forbiden to even go over that wall. One day her father takes her on a trip to Bridewell. There she finds a magical room, a underground passage, and magical creatures that only she can see. Her goal is to take down the wall that kepps them trapped. If she does??? Well you'll just have to read it then.....