The second layer of Arborea, Ossa is the realm of the oceanic quest, in contrast to Olympus as the realm of the landborne quest. This land of stormy seas is dotted with islands bearing small settlements or single creatures separated by miles upon miles of water, and the open sea of Ossa is the very essence of "Here There Be Dragons". Though filled with threats of all varieties, Ossa doesn't lack for friendly natives. In the sea, tritons, selkies, aquatic elves, and merfolk all call Ossa home, as do, of course, the noviere. While there are a few dotted locations of interest overland, by far the most interesting areas are found far below the water's surface.
The seas of Ossa — known to its various inhabitants as the Endless River, the Abiding Sea, or Aquallor — immediately around its islands are for the most part very shallow, with the shelves sloping gently for hundreds and even thousands of feet before dropping off. This makes boating across Ossa somewhat more hazardous than in some aquatic realms, though this is often merely just another obstacle to surpass. Beyond the shallow regions but still at the surface, a number of creatures both friendly and dangerous make their homes. Cetaceans of all sorts can be found here, from basic life such as dolphins and whales, to intelligent varieties like the balaenas or delphons, to truly massive leviathans. Nearly any sort of aquatic hazard one can imagine could be found somewhere within Ossa as well - dragon turtles, zatarans, giant squid, and other beasts all enjoy its waters. Some claim that should you sail enough, you may even reach the fabled edge of the world here, the waters of Ossa pouring in endless waterfalls into the great beyond. There are other ways to pass beyond the boundaries of Ossa, of course. Much as the reverse, one may reach Olympus from Ossa by simply sailing far enough in the proper direction, eventually reaching the craggy shorelines of that layer. Pelion can also be reached here through travel, though this is far more difficult; some few islands bear underground ruins which, if explored deeply enough, eventually emerge within that endless desert. These ruins seem to move as well, especially should word of their presence spread too far, for it is only the ancient secrets that reveal themselves in Pelion.
Beyond the shelves and beneath the surface, the waters of Ossa plunge to amazing depths, to the point that sunlight can't even penetrate the layers upon layers of water. However, though these depths are impressive, they are not infinite; all the seas of Ossa do seem to possess sea floors, even if for some these floors are miles below. Most of this layer's powers prefer to make their realms in these regions of the deep, away from the eyes of air-breathers.
Ossa serves as the terminus of the River Oceanus, though it holds many swirling portals back to the source, Thalasia, allowing a traveler easy access to the entire circuit. There also exist some vortices and maelstroms with portals to Lunia or the occasional Prime ocean, but especially to the plane of Water; Ossa is perhaps one of the most well-connected outer planar regions to an inner plane, and as such much Outer/Inner mercantile traffic passes through here. This hasn't yet spawned any large merchant cities above, as the local weather grows especially furious around any attempts at founding large cities wholly overland, the massive thunderstorms, powerful floods, and even the rare tsunami making it almost impossible for any surface settlements to grow beyond the size of village. Elshava, a major mercantile city larger than most gate-towns, but still out of the way and minor enough to not be counted amongst planar metropolises, is the sole exception, getting no more impact from the weather than anywhere else; most likely because it spans both above and below water, floating in the open sea away from any island. Within the deepest depths, a good few towns get helpful economic boosts from the interplanar traffic; most prominently, the city of Corilla, an aquatic elf settlement in the realm of Caletto, which lies directly on a major trade route between the two.
- Manual of the Planes, pg.146
- Planes of Chaos - Book of Chaos, pp.50-54