The Real Largest Mirror in the world

             The large area, clear skies and exceptional surface flatness make the Salar an ideal object for calibrating the altimeters of Earth observation satellites. When covered with water, this extraordinary place becomes one of the largest mirrors on Earth.

                Salar de Uyuni (salar is salt flat in Spanish) is currently the world’s largest salt flat at 10,582 square kilometers (4,086 sq mi). Actually, some 30,000–42,000 years ago, the area was part of a giant prehistoric lake, Lake Minchin. When it dried, it left behind two modern lakes and two major salt deserts, Salar de Coipasa and the larger Salar de Uyuni.

    When it rains, this flat surface forms an incredible "mirror" that is so big, and so reflective, that governments actually focus on it to calibrate their satellites!

             In the low-rain period from April to November, due to the absence of industry and its high elevation, the skies above Salar de Uyuni are very clear, and the air is dry. It has a stable surface which is smoothed by seasonal flooding (water dissolves the salt surface and thus keeps it leveled).  

 Sources : Wikipedia & Google Images