Shinkiro are a supernatural phenomenon in Japanese folklore derived from a Chinese legend. They appear as an illusion out to sea of a beautiful city with pagodas and tall towers. No matter how much you try to approach them they keep receding into the distance. Apparently they are created by a breed of giant supernatural yokai clams related to dragons. The mirage they create mirrors the mystical underwater palace of the dragon king. The word shinkiro (蜃気楼) means mirage in Japanese.

🎨1. Matthew Meyer (via yokai.com)