The Sundered Sky
A lone tree stands tall, surrounded by a ring of islands floating atop of sea of clouds. Below lies the Sunken Lands, a grim and cruel world ruled by the servants of an angry god. The World Tree connects these two places, lifting up land from the world below to create new islands, and lowering them back down when their magic is spent.
These two lands were once one, until the Great Sundering split the land, and began an eternal battle for the fate of all life. Only a small part of the world was saved when the World Tree lifted the islands into the sky, filling the space left behind with the Sea of Clouds and creating the Lands Above. Now every thousand years the Lands Above must fight a desperate battle against the forces of the Sunken Lands the protect what's left of the world, but they are slowly losing.
Infighting on the surface, and the constant struggle against the Sunken Lands has meant that more islands have sunk below, than new ones have arisen, and many fear that unless a permanent solution is found, eventually all shall be lost. Some look below, exploring the deepest reaches of the Sunken Lands searching for ancient knowledge that has long since been lost. Others look above, hoping to climb the World Tree and search for answers among the Divine Realms. Others still do neither, and just try to survive in the harsh world that is the Sundered Sky.