Longer ago than anyone can remember, a primordial forest stood sentinel over the massive, forgotten island of Terrene, which protrudes like a mighty ship of enormous proportions from the choppy waters of the Sea of Mists.
When you think about it, it's quite easy to imagine why this land might have been lost to time. The dense, unabating mists which gave the sea its name, shrouded the island in a cloak of invisibility, and wary seamen were hesitant to risk their ships or their crews by traveling blind into this hidden realm.
Even if the seaworthiest of ships somehow managed to blunder through the perilous mists, they would find only turbulent, unrelenting waters that would easily dash a ship to bits in a matter of minutes. If by some very unlikely chance, a courageous and wise sea captain somehow made his way through the waters, he would find steep, impenetrable mountains that formed the outer perimeter of the island, barring him from landing.
As eons passed and this secret world was remade a thousand times over, the giant mountains grew ever taller. The vast ancient forest withstood the test of time, reaching towards the light, becoming denser and more menacing.
As time continued to pass, changes were inevitable, and so it was with Terrene. Storms, lightning strikes, wind, drought, ever-changing temperatures, erosion, and much more played their parts. The land became more diverse, with flowing grasslands, deep valleys, steep mountains, magical woodlands, and rivers traversing it from mountain range to mountain range.
Then, almost as though they fell from the sky, creatures of every ilk began to make their home on Terrene. Your guess is as good as mine as to how they got there, but there they were, nonetheless. Elves, piskies, gnomes, fearsome wolves, giant eagles, mighty dragons, warrior insects, and the wizard dragon master himself.
And after many, many more years had gone by, humans appeared. Only a few at first, but over the years there were more, and more, and more. Still, for all that, the island remained sparsely populated and peaceful by most measures - until evil entered stealthily one day and threatened the island and its inhabitants with annihilation.