The Lake of Mists and Veils is a large body of water in northeastern Avistan, bordered by the nations of Brevoy, Mendev, and Numeria. In Brevoy, people simply call it "The Lake."  The lake is the source of the mighty Sellen River, and much of the trade and transportation in the region travels along the river, the lake, or both. The lake's name originates from how, at the onset of winter, the warm water "steams" as the chill of night sets in, and then the water burns off in the morning. 
Dark whispers in Brevoy speak of powerful inhabitants who live beneath the lake's waters—the true masters of the land of Issia—who emerge from the depths at night to make dreadful bargains with local villagers. What validity these claims hold, however, remains ambiguous.