Shadow Chaser by Alexey Pehov

Saddened because they have left one of their number in a grave in the wilderness, Harold and his companions continue their journey to the dreaded underground palace of Hrad Spein. There, knowing that armies of warriors and wizards before them have failed, they must fight legions of untold, mysterious powers before they can complete their quest for the magic horn that will save their beloved land from The Nameless One. But before they can even reach their goal, they must overcome all manner of obstacles, fig