In the middle of the rainy season, a stretch of Bolivia’s high desert turns into the largest mirror on the planet — a thin, perfectly still sheet of water spread across ten thousand square kilometers of salt, so exact that the sky and the ground become impossible to tell apart

Salar de Uyuni sits at roughly 3,650 metres on the Altiplano, a high plain in the central Andes with no drainage outlet. Between December and April a shallow film of water settles on the salt crust and reflects everything above it, horizon to horizon. Why the salt is so flatThe European Space Agency puts the variation in surface elevation across the entire salar at under one metre. Across 50 kilometres of salt, the ground rose and fell by a grand total of 77 centimetres. Because the salar is levelled by water that settles along that surface, the salt has slowly taken its shape.