Barovia

At the foot of Mount Baratok, nestled in the misty forest of Vallaki Valley, is a large lake. The water is perfectly still and dark, reflecting the black clouds overhead like a monstrous mirror. An Undead Aboleth was trapped within Lake Zarovich when the realm was formed. It attracts spellcasters, usually Warlocks, promising them power and riches if they either find a way for it to escape or kill the Mad Mage of Mount Baratok, who plagues it with lightning bolts. The Aboleth is far too fearful of Strahd to act and show its presence, preferring to stay idle at the bottom of the lake until it is time to take its freedom