The largest mirror in the world is in Bolivia, it is called salar de uyuni. It is known as largest mirror in the world because it’s ground reflect that sky. This beautiful desert is formed because It containes about 10 billion tonnes of salt. Basically, the high plateau here had no distributing installations, which meant that water from the surrounding mountains once collated to form a giant lake. High salinity meant duting this, prehistoric lake has long since evaporated under the fierce Andean sun, and a thick crust of salt remains, forming what we now recognise as the salt flats of Salar de Uyuni. But you can not see this view every time. The best time to visit Salar de Uyuni is depends on what kind of view you are looking for. For the best climate, I recommend you to visit between July and October, but for a better chance of seeing the reflective surfaces, I recommend you to visit between March and April.