Sea of Silver Light - Tad Williams

Otherland - a display of mankind's extraordinary intellect, a multi-dimensional universe built by the geniuses of the twenty-first century and controlled by the private cartel known as the Grail Brotherhood, powerful and ruthless. But now Otherland is out of control. Fleeing through broken realities, a small band of adventurers struggle to avert the nightmare that Otherland could become. The only hope may lie in an alliance with their enemy. But time is running out - and Otherland's most terrifying secret is yet to be revealed.