High in the mountains of Bolivia lies a place where the Earth disappears into the clouds. The Salar de Uyuni, the world’s largest salt flat, stretches across more than 10,000 square kilometres. After rain, its surface transforms into a flawless mirror that reflects the entire sky — making it look as though you’re walking through the heavens.
This breathtaking illusion is created by a simple trick of physics. Salar de Uyuni is made of tightly packed salt crystals left behind by an ancient lake that dried up thousands of years ago. When rainwater collects on its perfectly flat surface, it forms a thin, smooth layer only a few centimetres deep. Because the layer is so shallow and even, it reflects light almost perfectly — turning the ground into a vast, natural mirror.
The salt crust beneath the water is so white and level that NASA uses it to calibrate satellites. The flatness is so extreme that the entire 10,000-square-kilometre surface varies by less than a metre in height.
During the dry season, the mirror vanishes, leaving behind an endless expanse of white polygons formed by salt crystals. In the wet season, the illusion returns — sky below, sky above — blurring the boundary between Earth and air.