The Outside by Jack Batchen

SPFBO9

The Vale is safety. The Vale is prosperity and protection. Yet the Words of Life themselves state that every young man must leave the safety of the Vale at age sixteen and cross the deadly wasteland that is the Outside. Kaere has lived her whole life within the mountain walls of the Vale, dreaming of somewhere else, anywhere else, dreaming of a future that is anything but being one wife among many to a husband she barely knows.
So when her oldest and dearest friend stumbles back through the mountain pass seven years after he left, battered and bruised, declaring that the Outside is alive, moving, eating places of safety like the Vale, all Kaere can see is a chance at another life, a life Outside the Vale Walls. But when she follows Janzen back Outside — against his wishes — she realises that everything she thought she understood is not as it seems, including her oldest friend.