The Sea of Clouds is a vast airy expanse.  Land masses, called bergs and cays hang suspended within the Sea of Clouds.  Cities and nations are built upon the surfaces of the bergs and cays. These floating land masses are collectively known as the many worlds.  The air within the Sea of Clouds is usually safe to breath.

The Sea of Clouds is roughly spherical in shape, with bergs and cays dotting it throughout.

At the center of the Sea of Clouds is a firey sphere called the Furnace.  The Furnace provides heat, light and produces magma like matter that eventually forms into new bergs and cays.

The Sea of Clouds is orbited by the Nine Suns.  Usually, only one sun is visible in the sky at any one time. 

While the Sea of Clouds is mostly air, it isn't empty.  In between the many worlds are vast fog banks, flying creatures, hardened alch deposits and massive storms.  People travel the Sea of Clouds using Cloud Cruiser.  Though travel is common, the Sea of Clouds is so large that it is widely believed that no one has explored the whole of it.