Salar de Uyuni, Bolivia

Perched at nearly 12,000 feet, this salt flat is the largest in the world. The ancient lake bed spans 3,900 square miles, so featureless that geophysicists have compared it to an ocean with no waves. While the visual expanse can be overwhelming, the silence is equally striking. The flats are visited by breeding flamingos and bands of salt miners, but they remain relatively untrammeled. That might change with growing global demand for batteries: Major lithium reserves are believed to lie under the salty surface.