Gods of Fire and Thunder — Fred Saberhagen

Haraldur the Northman wants nothing more to do with adventure and gods. Returning to his homeland for the first time in many years, he hopes to settle down on a farm of his own--until he comes across an impenetrable wall of eldritch fire.

Beyond the towering flames, Hal is told, lies a beautiful Valkyrie trapped in an enchanted sleep, as well as, a golden treasure beyond mortal reckoning. Hal is easily tempted by the gold and joins a lovesick youth in his quest to awaken Valkyrie. But to find a way past the fiery wall, they must brave gnomes, ghosts, and the wrath of the gods themselves. For a mighty battle is brewing, and Hal soon finds himself caught up in a celestial conflict between Thor the Thunderer, Loki the Trickster, and most powerful of all, Wodan, the merciless Lord of Battles.