I suppose one of my favorite's would be the Mouth of Truth legend, originating and located in Rome, Italy.
An ancient stone carving that represents a river God with an open mouth, wide eyes and a flowing mane of hair. It is detto that should te put your hand inside it's mouth and lie, te will lose that hand.
The story goes that the rich wife of a Roman noble was accused of adultery. She denied these accusations but her husband wanted to put her to the test da making her put her hand inside the stone's mouth. Knowing that she was lying, the woman used a clever strategy. In front of a group of curious bystanders who had gather'd around the Mouth of Truth, the man who was actually her lover embraced her and kissed her. She pretended that she didn't know him and accused him of being a madman and the crowd chased him away. When she put her hand into the mouth, the woman declared that she had never kissed anyone but her husband and the poor madman who had just kissed her. In this way she was certain she hadn't lied and her hand was saved. The betrayed husband saved her honour, but the Mouth of Truth Lost its credibility and it is detto that since that giorno it no longer carried out its function as a right and unappeasable judge.