To Conquer Chaos — John Brunner

The barrenland lay on the face of the world like a sore, nearly round, more than three hundred miles in circumference. It had been there so long that it was endured, as were the twisted monsters that wandered out of the barrenland and killed. Conrad, living on the dge, had visions of a time when the barrenland was a rich region full of powerful, magical people- people who travelled to other worlds. He was ruled by a burning need to know what none could tell him: the explanation of the mysterious visions that had plagued him all his life. Then he met Jervis Yanderman, a soldier who knew of these visions. Yanderman was convinced there was an island in the barrenland where people still clung to life...