Welcome to the Arctic: months of darkness, frigid temperatures, little food to be found or grown. Despite this, four million people live their lives in this environment. Meet them and witness their remarkable tales of survival in the world's harshest climate.

The rainforest is home to more species of plants and animals than any other habitat on the planet. For the humans who call this environment home, life requires skill, ingenuity, and sheer bravery.

From lush cloud forests to bare summits, many people make their homes in the extreme altitudes of the world's mountain ranges. Explore the extraordinary ways life is sustained in this world of thin air and few resources.

Grasslands feed the world. Over thousands of years, humans have learned to grow grains on the grasslands and domesticate the creatures that live there, propelling our population to almost seven billion people in the process.

Rivers provide the essentials of life: fresh food and fresh water. They act as natural highways and enable humans to live in just about every environment on Earth. Rivers are not to be taken for granted, however, as they freeze, flood, and sometimes dry up - disappearing entirely!

A look at the man-made environment: the city. Over half of the world's population now lives in the urban jungle. The city is built to keep untamed nature out - but nature can't be pushed away. From bed bugs sucking blood at night to rats in our restaurants, many animals have adapted to a life in man's creation.