Poseirius (pronounced poh-SIGH-ree-us) is an underwater city within the Chaska Sea, less than fifty miles from the southern coast of Thadria. Nestled amongst a dense kelp forest, the buildings of Poseirius are ornate towers that nearly touch the surface of the sea. There are very few areas within the city in which air-breathers could safely exist. Even if it were habitable to surface-dwellers, the merfolk of Poseirius rarely allow outsiders access to their settlement under the waves. Ships heading to port in Orhassu usually stick close to the shores and give the city a wide berth.