The Worldwrights by Max Grant
Available for free download as an audiobook from Podiobooks: http://www.podiobooks.com/title/the-worldwrights
The underlying premise of this book is of an SF nature: an artificial world built when a race's home planet was destined to be destroyed. There's engineered life-forms and other remnants of a hi-tech civilization. But as so many authors seem to like to do, this is thousands of years later and the origins of the world is more or less a legend, the inhabitants are living pre-industrial lives and so on. The technology has been largely forgotten and viewed in the mystical way a cargo cult conceived of the planes and supplies of WWII. Much of the story is more reminiscent of fantasy. A bad guy of demigod proportions. A single hero who begins his quest walking through a jungle armed with a knife and a spear. On his journey he encounters fantasy-like life-forms such as walking/talking trees, a man made out of stone, flying lions and a sea monster; and things like a lake that takes the minds of people who go into it (the "mindless" people live zombie-like lives and their disembodied "minds" continue like spirits in the lake).
The first half of the book is a journey from where the protagonist wakes to a central city. It begins as a long trek by foot through wilderness. Then there is a trip on a sailing ship. Along the way he meets creatures of a mythical sort and encounters objects and situations resembling the patterns and symbolism of ancient legends. Battle is done by bow and arrow, spear, knife and the like. There is a mystical-seeming translation of languages between different kinds of beings. Various activities seem to be "mind over matter".
There is a part of the middle of the book in which the human good guys battle armies of "demons". Then a central group of five good guys journey to the dark lands which are the source of the demons and other bad changes to the world. The members of this group are like demigods of ancient lore or superheroes of comic books - each with their particular super-powers. But the book tells us what sets them apart most is their faith of heart.
It seems to be an attempt to situate a story like "Lord Of The Rings" or an ancient heroic epic on Ringworld or Rama. Personally, this still leaves me feeling I'm reading Fantasy. Yes, if you read through the book, you'll find there is an underlying SF premise that has merely been hidden most of the time. This may work for those who enjoy fantasy. For me, it was like having a piece of gold jewelry that is plated with tin on the outside except in a few places where you're allowed to glimpse gold beneath. I don't see the point in that.
There is a scene where we are told that the reason the hero must use a certain means to get to a certain place is because this arrangement prevents the bad guy from getting there. But when the hero does this, the bad guy is able to chase him there. The book has plenty of such inconsistencies. My impression is that fantasy readers don't tend to mind this sort of thing as much as some readers. Perhaps you should judge your own tolerance for these inconsistencies.