Memory, Sorrow and Thorn, book 3: To Green Angel Tower, part 1
Tad Williams1993

As the evil minions of the undead Sithi Storm King prepare for the kingdom-shattering culmination of their dark sorceries and King Elias is drawn ever deeper into their nightmarish, spell-spun world, the loyal allies of Prince Josua desperately struggle to rally their forces at The Stone of Farewell. And with time running out, the remaining members of the now-devastated League of the Scroll have also gathered there to unravel mysteries from the forgotten past. For if the League can reclaim these age-old secrets of magic long-buried beneath the dusts of time, they may be able to reveal to Josua and his army the only means of striking down the unslayable foe.

But whether or not the League is successful in its quest, the call of battle will lead the valiant followers of Josua Lackhand across storm tossed seas brimming with bloodthirsty kilpa...through forests swarming with those both mind- and soul-lost... through ancient caverns built by legendary Dwarrows...to the haunted halls of Asu'a itself—the Sithi's greatest stronghold!