The Lake of Serenity was a playable location in Blood Omen: Legacy of Kain.
The Lake was a large body of water South of Avernus . It had a large island at its centre upon which most of the walled city of Willendorf was built; although much of the Willendorf settlement and it's Provincial Mines were to the east of the Lake and connected to the City by a bridge.
The Lake of Serenity is aptly named, given the peaceful and prosperous nature of the kingdom of Willendorf. This serenity would not have lasted had The full implications of the Legions of the Nemesis victory over the Army of the Last Hope in the Battle of the Last Stand impacted upon its residents.