Salar de Uyuni at 10.5 thousand square kilometers (4,000 sq mi) is the world's largest salt flat and is located in Bolivia. Salar de Uyuni (and the smaller Salar de Coipasa) are what is left from a series of prehistoric lakes, the last of which dried out about 13,000 years ago.
The desert is at an altitude of 3.7 km (12,000 ft) and is basically a pool of brine 2 to 20 meters (7 to 66 ft) deep covered by a hard salt crust with a thickness varying between tens of centimeters to a few meters.
In the wet season lake Titicaca overflows and discharges into Salar the Uyuni (via other intermediate lakes), which means there are a few cm of water on top of the salt crust.
I have picked August/September (the dry season) specifically to avoid this: Average precipitation is then just a fraction of that during the wet season (December to March). However, temperatures are also much lower with an average surface temperature in July/August of -10C (14 F). So I expect night-time temperatures to drop to -20C (-4 F).
Photo from Wikipedia, author Anouchka Unel
Photo from Wikimedia Commons, author Martin St-Amant
Photo from Wikimedia commons, author Lion Hirth
Map of Bolivia. Salar is the white bit at bottom left.
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