About 15-20 years ago I read a book about a young boy / man who lives in a sheltered community. They are protected by some sort of force field and most if not all of them can control some sort of shadow. He does something and gets thrown into a hole to "rot" there by one of the highest members of the community. But thanks to his shadow he manages to escape out of the hole and the communities place (an old fortress?).
He then gets into the surrounding lands and befriends a girl who travels on a ship that travels over land (some sort of pirates or junk gatherers). They hate those shadow users. Still though she helps him.
He then wants to get back to the community to warn them about the plans of their leader (which lead to their destruction / death).
From what I also remember his father was also once thrown into the hole and died there?
That is about all I remember there sadly.