River of Blue Fire — Tad Williams

In many ways it is humankind's most stunning achievement: a private, multidimensional universe built over two generations by the greatest minds of the twenty-first century. But this most exclusive of places is also one of the world's best kept secrets, created and controlled by a private cartel known--to those who know of their existence at all--as The Grail Brotherhood. Though their purpose in creating Otherland is a mystery, they have exacted a terrible price from humanity in the process, and even their highly organized global conspiracy cannot hide the nature of their. crimes forever.

And now a small band of adventurers have penetrated the veil of secrecy that prevents the uninitiated from entering Otherland. But having broken into the amazing worlds within worlds that make up this universe, they are trapped, unable to escape back to their own flesh-and-blood bodies in the real world. And as dangers and circumstances split their party into small, widely scattered groups, their only hope of reuniting lies in returning again and again to the River that flows--in one form or another--through all the worlds.