Medusa

She was once a young beautiful guardian of Athena's temple before she met Posidon. She wasn't interested in Posidon but was forced on by him. Athena disgusted by this action, curses Medusa (as she couldn't punish Posidon considering he's a greater god than Athena herself.) into a snake haired serpent that can turn most creatures into a stone at will with just a look into her eyes, so that she wouldn't be forced on again. She currently resides in one of the ancient Greek temples and petrifies any intruders who dares to enter, including you which you decide to explore the abandoned temple.