Answer: Maldives

Around the world you’ll find countries that are close to sea level and not particularly mountainous, so their average elevation is, across the board, pretty low. You’ll also find mountainous countries where the entire country is far above sea level, but the general change from one elevation to another is not particularly dramatic.

Then, in the category of undeniably flat-as-can-be you have a country like Maldives. Maldives, a vast chain of islands in the Indian Ocean, is the flattest (lowest) country on Earth. Maldives has such little change in elevation over the entire island chain that if the wind blows a sand dune to a height of 3 meters above sea level, that sand dune temporarily becomes the highest natural peak in the island chain (which averages a mere 1.5 meters above sea level with a highest point of only 2.4 meters).