The Mist Sea, also known as the Nidavellir, is a sea of mist and fog that fills a massive crater at the center of the continent where Path to Power and Drowtales: Moonles Age takes place.
It is said that the Nidavellir was formed when a shard of one of the moons crashed into the surface of the planet and that it is because of this shard the Nidavellir infuses a certain amount of mana into the mists that spread from it's shores. Whatever the reason, it is known that close proximity to the Nidavellir slows down the detriment of Mana Deprivation and without it colonization of the surface would be much more difficult.
There are a few outposts and settlements within the Nidavellir itself, although the only contact the Tei'kaliath have had so far is with a Nal'Sarkoth outpost close to Amaranth.