The Sunset Warrior & Shallows Of Night by Eric Lustbader (Sunset Warrior Cycle)

Under the layer of eternal ice that bound the entire surface of the planet, there is the kingdom of the gloomy Freehold, where power and the sword rule. Ancient Machines that give life to the inhabitants of the underworld fail one after another. But in the doomed land there is one man whose spirit is not broken, whose swift sword brings death to enemies. A rebel at heart, he excelled in the ancient arts of love and war. In search of truth, he goes into the void and further - on the other side of the void. His name is Sunset Warrior.