The Wood Beyond the World. A fantasy novel by William Morris, with the element of the supernatural, and thus the precursor of fantasy literature.

When the wife of Golden Walter betrays him for another man, he leaves home on a trading voyage to avoid the necessity of a feud with her family. However, his efforts are fruitless, as word comes to him en route that his wife's clan has killed his father. As a storm then carries him to a faraway country, the effect of this news is merely to sunder his last ties to his homeland. Walter comes to the castle of an enchantress, from which he rescues a captive maiden in a harrowing adventure (or rather, she rescues him).
They flee through a region inhabited by mini-giants, and eventually reach the city of Stark-wall, whose custom, when the throne is vacant, is to take the next foreigner to arrive as ruler. The late king having died, Walter and his new love are hailed as the new monarchs. The two are married and presumably live happily ever after...