Salar de Uyuni, the largest salt flat in the world.
IIRC there’s one or two big, though short, “rainy season(s)”. Since everything is so dry and hard, the water doesn’t absorb into the ground quickly, which creates this gigantic “lake” that’s only an inch or so deep.
There’s a rainy season but at its peak you won’t be able to do the trip. You want to go after the rainy season but before it all dries out. That way you get the best of both worlds; you can see the endless salt on the dry side and the beautiful mirror on what’s still wet.