A mirage is a unique phenomenon of refraction in the atmosphere that takes place under special geographical and climate conditions. Mirages often occur during the winter and spring in the Arctic and during the summer in the desert. They can also occur along the coast or in the sky above rivers and lakes. The most famous mirages in China occur in Penglai in Shandong Province. They look like castles in the sky and have been called the ‘celestial land of Penglai’.