The Golden Door — Emily Rodda

Three magic doors you here behold.
Time to choose: Wood? Silver? Gold?

Rye stands before three Doors, about to step out into the unknown. He's lived his whole life safe inside the enormous wall that rings the city of Weld and protects against the terrible dangers outside. Now, Weld is under attack from skimmers, flying beasts that kill in the night. If the enemy sending the skimmers isn't found, the citizens of Weld are doomed.

But that's not why Rye has volunteered on a mission to leave Weld and stop the skimmers. His real goal is to find his two older brothers, who volunteered before him and never returned. Now Rye must open a Door and begin a perilous quest that could save his brothers... or cost his life.