Curious places in Mauritania

A 50 km wide bullseye in the Sahara visible from space. Scientists thought it was a meteor crater, but it's a deeply eroded rock dome that rose and collapsed, exposing concentric rings of geological layers. Some claim it's the remains of Atlantis.

4,000-year-old stone-walled villages where refugees from the dying Sahara invented West African agriculture. As the desert swallowed their homeland, they learned to cultivate millet - a survival strategy that would feed millions.