Complex sentence: The Postman, Abby, and a small group of postal carriers travel to Bridge City, built on an old dam wall, which is one of the few peaceful sanctuaries that has also been getting mail from other post offices.
Split into simpler sentences: The Postman, Abby, and a small group of postal carriers travel to Bridge City. Built on an old dam wall, it is one of the few peaceful sanctuaries that had also been getting mail from other post offices.