Wildest: India

Covering 125,000 square miles, India's Thar desert is one of the harshest places on Earth. Desiccating winds and a near-permanent drought has earned this unforgiving land another name: the region of death.

The Ganges is the longest river in India. It flows from the glaciers of the Himalayas all the way down to the Bay of Bengal. It's a lifeline to wild animals, from rhinoceros and river dolphins to otters and gharial crocodiles.

The Himalayas run across 1550 miles of north India. The Himalayas' rugged highlands offer little direct refuge to humans, and in the shadow below, over a billion people in India rely on the mountains for survival.

The Western Ghats are a spine of mountains that lay claim to being one of the most bio-diverse places in the world. In the east, tigers and wild dogs compete for prey in the dry forests. All the while, the western Ghats hold the key to life across southern India.

Northeast India is an anthropological paradise; there is no other place on Earth with so many different ethnic groups. The forests are filled with mysterious tribes whose lives are dictated by the rain and the seasonal fruits of the forest.