(image credit: Joachim Pietsch)
Salar de Uyuni is the world's largest salt flat, high in the Andes mountains in Bolivia. In the rainy season when it is covered with a thin sheet of water, it reflects the sky.
Due to its large size, smooth surface, high surface reflectivity when covered with shallow water, and minimal elevation deviation, Salar de Uyuni makes an ideal target for the testing and calibration of remote sensing instruments on orbiting satellites used to study the Earth.
The salt flat contains an estimated ten billion tons of salt, in a layer ten feet thick. See more pictures and videos at Fogonazos. Link -via Reddit