Lock Lake lies to the east of Britain, and to the far south of Lost Hope Bay. Once part of the Great Sea, this inland lake has now been mostly separated from the nearby ocean to the south by Britannia's changing geography, and is now only connected by a shallow river . The Shrine of Compassion lies on the southwestern shores of this lake, while the peaceful town of Cove finds itself nestled along the lake's eastern shores.
In Ultima IV, if a frigate had the misfortune of being captured by one of the great whirlpools plaguing Britannia, the sailors would find themselves transported to Lock Lake. During Ultima V, the lake could be accessed by a smaller skiff. By Ultima VI, it had become possible to cross the river connecting Lost Lake to the sea by foot, thus allowing easier access to the city of Cove. During Ultima VII, the lake had become extremely polluted, but a law passed by Miranda ended this destruction by the Britannian Mining Company. By Ultima Underworld II, the inhabitants of Cove were still busy with cleaning the lake.